TST: tests compat on 2.6
when using slow enabled on 2.6-32 bits on windows

```
======================================================================
ERROR: test_ts_plot_format_coord (pandas.tseries.tests.test_plotting.TestTSPlot)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win32-2.6\pandas\tseries\tests\test_plotting.py", line 143, in test_ts_plot_format_coord
    check_format_of_first_point(annual.plot(), 't = 2014  y = 1.000000')
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win32-2.6\pandas\tseries\tests\test_plotting.py", line 140, in check_format_of_first_point
    self.assertEqual(expected_string, ax.format_coord(first_x, first_y))
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win32-2.6\pandas\tseries\plotting.py", line 86, in <lambda>
    ax.format_coord = lambda t, y: "t = {}  y = {:8f}".format(Period(ordinal=int(t), freq=ax.freq), y)
ValueError: zero length field name in format
```

I think this test just needs to be changed as this is not supported on 2.6

```
======================================================================
ERROR: test_boxplot (pandas.tests.test_graphics.TestDataFramePlots)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\Users\Jeff Reback\Documents\GitHub\pandas\build\lib.win32-2.6\pandas\tests\test_graphics.py", line 1341, in test_boxplot
    self.assertRaisesRegexp(
AttributeError: 'TestDataFramePlots' object has no attribute 'assertRaisesRegexp'
```

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.6.6.final.0
python-bits: 32
OS: Windows
OS-release: 7
machine: x86
processor: Intel64 Family 6 Model 42 Stepping 7, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: None
nose: 1.3.0
Cython: 0.19.2
numpy: 1.6.2
scipy: 0.10.1
statsmodels: 0.5.0
IPython: 1.1.0
sphinx: None
patsy: None
scikits.timeseries: None
dateutil: 1.5
pytz: 2012c
bottleneck: 0.7.0
tables: None
numexpr: 2.0.1
matplotlib: 1.1.1
openpyxl: None
xlrd: 0.9.2
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
bq: None
apiclient: None
rpy2: None
sqlalchemy: None
pymysql: None
psycopg2: None
```
