plot dies with tzoffset exception
Moved original posted by @Bklyn in #2658 to here

I find I need to call tz_convert() on my DataFrame before I can plot it.  By default the index tz is a "tzoffset" I get an exception when plottng.

``` python

AttributeError: 'module' object has no attribute 'tz'

d=pd.read_csv('vix.dlmp.csv', parse_dates=[0], index_col=0)

d.index.tz
Out[23]: tzoffset(None, -18000)

d['2012-12-28 09:30:15-05:00':]
Out[24]: 
<class 'pandas.core.frame.DataFrame'>
DatetimeIndex: 981 entries, 2012-12-28 09:30:16.311000-05:00 to 2012-12-28 09:59:46.518000-05:00
Data columns:
Und            981  non-null values
BidPrice       981  non-null values
AskPrice       981  non-null values
TradePrice     981  non-null values
BidSize        981  non-null values
AskSize        981  non-null values
TradeSize      981  non-null values
T0             981  non-null values
T1             981  non-null values
T2             981  non-null values
T3             981  non-null values
T4             981  non-null values
T5             981  non-null values
dtypes: float64(9), int64(3), object(1)

d['2012-12-28 09:30:15-05:00':].plot(y=['BidPrice', 'AskPrice', 'TradePrice', 'T0', 'T1'],style=['g', 'b', 'r', 'k--', 'g--'],drawstyle='steps',figsize=(16,9))

￼
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-25-d7985a840c41> in <module>()
----> 1 d['2012-12-28 09:30:15-05:00':].plot(y=['BidPrice', 'AskPrice', 'TradePrice', 'T0', 'T1'],style=['g', 'b', 'r', 'k--', 'g--'],drawstyle='steps',figsize=(16,9))

/usr/local/lib/python2.7/dist-packages/pandas/tools/plotting.pyc in plot_frame(frame, x, y, subplots, sharex, sharey, use_index, figsize, grid, legend, rot, ax, style, title, xlim, ylim, logy, xticks, yticks, kind, sort_columns, fontsize, secondary_y, **kwds)
   1419                            grid=grid, logy=logy, secondary_y=secondary_y,
   1420                            title=title, figsize=figsize, fontsize=fontsize,
-> 1421                            **kwds)
   1422 
   1423     plot_obj = klass(frame, kind=kind, subplots=subplots, rot=rot,

/usr/local/lib/python2.7/dist-packages/pandas/tools/plotting.pyc in plot_series(series, label, kind, use_index, rot, xticks, yticks, xlim, ylim, ax, style, grid, legend, logy, secondary_y, **kwds)
   1504                      secondary_y=secondary_y, **kwds)
   1505 
-> 1506     plot_obj.generate()
   1507     plot_obj.draw()
   1508 

/usr/local/lib/python2.7/dist-packages/pandas/tools/plotting.pyc in generate(self)
    731         self._compute_plot_data()
    732         self._setup_subplots()
--> 733         self._make_plot()
    734         self._post_plot_logic()
    735         self._adorn_subplots()

/usr/local/lib/python2.7/dist-packages/pandas/tools/plotting.pyc in _make_plot(self)
   1063             lines = []
   1064             labels = []
-> 1065             x = self._get_xticks(convert_period=True)
   1066 
   1067             plotf = self._get_plot_function()

/usr/local/lib/python2.7/dist-packages/pandas/tools/plotting.pyc in _get_xticks(self, convert_period)
    878                 values for xaxis, several actions are already taken by plt.
    879                 """
--> 880                 x = index._mpl_repr()
    881             else:
    882                 self._need_to_set_index = True

/usr/local/lib/python2.7/dist-packages/pandas/tseries/index.pyc in _mpl_repr(self)
    474     def _mpl_repr(self):
    475         # how to represent ourselves to matplotlib
--> 476         return tslib.ints_to_pydatetime(self.asi8, self.tz)
    477 
    478     def __repr__(self):

/usr/local/lib/python2.7/dist-packages/pandas/tslib.so in pandas.tslib.ints_to_pydatetime (pandas/tslib.c:2998)()

AttributeError: 'tzoffset' object has no attribute '_transition_info'

In [26]: d=d.tz_convert('US/Eastern')

In [27]: d['2012-12-28 09:30:15-05:00':].plot(y=['BidPrice', 'AskPrice', 'TradePrice', 'T0', 'T1'],style=['g', 'b', 'r', 'k--', 'g--'],drawstyle='steps',figsize=(16,9))
Out[27]: <matplotlib.axes.AxesSubplot at 0x4c25a50>
```
