TestDataFramePlots.test_scatter fails with matplotlib v1.0.1
# Synopsis

The FreeBSD port for matplotlib has not yet been updated to v1.1.0. In the mean time, this test fails due to a default marker type ('.') that is unknown in matplotlib v1.0.1.
# Details
## Environment

```
# uname -a
FreeBSD REDACTED 9.0-STABLE FreeBSD 9.0-STABLE #0 r236450: Sat Jun  2 11:08:51 EDT 2012     root@REDACTED:/usr/obj/usr/src/sys/NIPPL  amd64
# pkg_info -oxQ pandas matplotlib
py27-matplotlib-1.0.1_4:math/py-matplotlib
py27-pandas-0.8.0.b2:math/py-pandas
```
## How to reproduce

```
#   nosetests -xv pandas.tests.test_graphics:TestDataFramePlots.test_scatter
test_scatter (pandas.tests.test_graphics.TestDataFramePlots) ... ERROR

======================================================================
ERROR: test_scatter (pandas.tests.test_graphics.TestDataFramePlots)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/pandas-0.8.0b2-py2.7-freebsd-9.0-STABLE-amd64.egg/pandas/tests/test_graphics.py", line 252, in test_scatter
    _check_plot_works(scat)
  File "/usr/local/lib/python2.7/site-packages/pandas-0.8.0b2-py2.7-freebsd-9.0-STABLE-amd64.egg/pandas/tests/test_graphics.py", line 301, in _check_plot_works
    ret = f(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pandas-0.8.0b2-py2.7-freebsd-9.0-STABLE-amd64.egg/pandas/tests/test_graphics.py", line 251, in scat
    return plt.scatter_matrix(df, **kwds)
  File "/usr/local/lib/python2.7/site-packages/pandas-0.8.0b2-py2.7-freebsd-9.0-STABLE-amd64.egg/pandas/tools/plotting.py", line 71, in scatter_matrix
    marker=marker, alpha=alpha, **kwds)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/axes.py", line 5738, in scatter
    raise ValueError('Unknown marker symbol to scatter')
ValueError: Unknown marker symbol to scatter

----------------------------------------------------------------------
Ran 1 test in 0.633s

FAILED (errors=1)
```
## Code analysis

[pandas/tests/test_graphics.py:252](https://github.com/pydata/pandas/blob/fde270b20861fbf36d3063d504fb299d0b58695b/pandas/tests/test_graphics.py#L252) does not specify a marker type.
[pandas/tools/plotting.py:22](https://github.com/pydata/pandas/blob/d7966d22f14375547e263347ec648dcba7b65617/pandas/tools/plotting.py#L22) defines `'.'` as the default value for the `marker`
[matplotlib/axes.py:5669-5682](https://github.com/matplotlib/matplotlib/blob/a9f3f3a50745a1ca0e666bb1b6d0b9d782553dd9/lib/matplotlib/axes.py#L5669-5682) list the marker types recognized in matplotlib v1.0.1.
## Suggested resolution

Choose a marker type available in matplotlib v1.0.1 (e.g. `'o'`).
