TST/CLN: Warnings from pytest 3.1+
New versions of pytest print a useful summary of warnings that aren't caught during the test run.
Here's a log from a couple days ago

<details>

```

=============================== warnings summary ===============================
pandas/tests/test_downstream.py::test_dask
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/dask/dataframe/__init__.py:3: DeprecationWarning: pandas.util.decorators is deprecated and will be removed in a future version, import from pandas.util
    from .core import (DataFrame, Series, Index, _Frame, map_partitions,

pandas/tests/test_downstream.py::test_xarray
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/xarray/core/formatting.py:16: FutureWarning: The pandas.tslib module is deprecated and will be removed in a future version.
    from pandas.tslib import OutOfBoundsDatetime

pandas/tests/test_downstream.py::test_statsmodels
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/statsmodels/statsmodels/compat/pandas.py:62: FutureWarning: The pandas.core.datetools module is deprecated and will be removed in a future version. Please use the pandas.tseries module instead.
    from pandas.core import datetools
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/patsy/util.py:652: DeprecationWarning: pandas.core.common.is_categorical_dtype is deprecated. import from the public API: pandas.api.types.is_categorical_dtype instead
    return safe_is_pandas_categorical_dtype(data.dtype)

pandas/tests/test_downstream.py::test_scikit_learn
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)

pandas/tests/test_downstream.py::test_seaborn
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/ipywidgets/widgets/widget_link.py:19: DeprecationWarning: Traits should be given as instances, not types (for example, `Int()`, not `Int`) Passing types is deprecated in traitlets 4.1.
    super(WidgetTraitTuple, self).__init__(Instance(Widget), Unicode, **kwargs)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/seaborn/seaborn/categorical.py:342: DeprecationWarning: pandas.core.common.is_categorical_dtype is deprecated. import from the public API: pandas.api.types.is_categorical_dtype instead
    elif is_categorical(y):

pandas/tests/test_downstream.py::test_pandas_datareader
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas_datareader/data.py:36: ResourceWarning: unclosed <socket.socket fd=17, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.7.36', 50017), raddr=('216.58.216.100', 80)>
    return GoogleDailyReader(*args, **kwargs).read()

pandas/tests/test_downstream.py::test_geopandas
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/fiona/drvsupport.py:143: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    ogrdrv_names = gdalenv.start().drivers().keys()
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/fiona/collection.py:145: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    self.env.__enter__()

pandas/tests/test_expressions.py::TestExpressions::()::test_integer_panel
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/panel.py:714: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, func)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/ops.py:1389: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, na_op)

pandas/tests/test_expressions.py::TestExpressions::()::test_float_panel
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/panel.py:714: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, func)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/ops.py:1389: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, na_op)

pandas/tests/test_expressions.py::TestExpressions::()::test_mixed_panel
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/panel.py:714: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, func)
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/ops.py:1389: DeprecationWarning: 
  Panel is deprecated and will be removed in a future version.
  The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
  Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
  Pandas provides a `.to_xarray()` method to help automate this conversion.
  
    return self._combine_const(other, na_op)

pandas/tests/dtypes/test_missing.py::test_array_equivalent_compat
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/numpy/core/numeric.py:2629: FutureWarning: elementwise == comparison failed and returning scalar instead; this will raise an error or perform elementwise comparison in the future.
    return bool(asarray(a1 == a2).all())

pandas/tests/frame/test_analytics.py::TestDataFrameAnalytics::()::test_corr_int_and_boolean
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/scipy/stats/stats.py:3577: RuntimeWarning: invalid value encountered in double_scalars
    size * (size - 1) * (size - 2))

pandas/tests/frame/test_analytics.py::TestDataFrameAnalytics::()::test_clip_mixed_numeric
  source:1893: DeprecationWarning: invalid escape sequence \d
  source:2464: DeprecationWarning: invalid escape sequence \(

pandas/tests/frame/test_operators.py::TestDataFrameOperators::()::test_boolean_comparison
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/internals.py:1153: DeprecationWarning: elementwise == comparison failed; this will raise an error in the future.
    result = func(values, other)

pandas/tests/indexing/test_coercion.py::TestFillnaSeriesCoercion::()::test_fillna_series_float64
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/internals.py:4785: ComplexWarning: Casting complex values to real discards the imaginary part
    nn_at = nn.astype(v.dtype)

pandas/tests/io/test_common.py::TestCommonIOCapabilities::()::test_read_fspath_all[reader7-os-/Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/tests/io/sas/data/test1.sas7bdat]
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)

pandas/tests/io/parser/test_network.py::TestS3::()::test_s3_fails
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/tests/io/parser/test_network.py:173: ResourceWarning: unclosed <ssl.SSLSocket fd=28, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.7.36', 50425), raddr=('54.231.33.187', 443)>
    read_csv('s3://nyqpug/asdf.csv')
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/tests/io/parser/test_network.py:173: ResourceWarning: unclosed <ssl.SSLSocket fd=27, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168.7.36', 50424), raddr=('54.231.40.83', 443)>
    read_csv('s3://nyqpug/asdf.csv')

pandas/tests/plotting/test_frame.py::TestDataFramePlots::()::test_line_colors
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/plotting/_core.py:179: UserWarning: 'colors' is being deprecated. Please use 'color'instead of 'colors'
    warnings.warn(("'colors' is being deprecated. Please use 'color'"

pandas/tests/plotting/test_hist_method.py::TestDataFramePlots::()::test_tight_layout
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/tests/plotting/test_hist_method.py:249: UserWarning: To output multiple subplots, the figure containing the passed axes is being cleared
    _check_plot_works(df.hist)

pandas/tests/plotting/test_misc.py::TestDataFramePlots::()::test_parallel_coordinates_with_sorted_labels
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/matplotlib/axes/_base.py:2917: UserWarning: Attempting to set identical left==right results
  in singular transformations; automatically expanding.
  left=0, right=0
    'left=%s, right=%s') % (left, right))

pandas/tests/plotting/test_series.py::TestSeriesPlots::()::test_pie_series
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/tests/plotting/test_series.py:296: DeprecationWarning: generator 'TestSeriesPlots.test_pie_series.<locals>.<genexpr>' raised StopIteration
    expected_texts = list(next(it) for it in itertools.cycle(iters))

pandas/tests/util/test_testing.py::TestAssertAlmostEqual::()::test_assert_almost_equal_edge_case_ndarrays
  /Users/taugspurger/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/dtypes/missing.py:308: DeprecationWarning: elementwise == comparison failed; this will raise an error in the future.
    return ((left == right) | (isnull(left) & isnull(right))).all()

-- Docs: http://doc.pytest.org/en/latest/warnings.html
```

</details>

Some of these will require updates to the test suite to just use the new behavior. Others should be explicitly caught with `tm.assert_produces_warning`. (I believe the downstream package warnings are already fixed in master for dask and statsmodels)