TST: test_ts_plot_format_coord   ValueError: Unknown format code 'f' for object of type 'str'
Only with ubuntu 12.04 i386:

```
======================================================================
ERROR: test_ts_plot_format_coord (pandas.tseries.tests.test_plotting.TestTSPlot)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/buildd/pandas-0.14.0+git345-g8cd3dd6/debian/tmp/usr/lib/python2.7/dist-packages/pandas/tseries/tests/test_plotting.py", line 138, in test_ts_plot_format_coord
    check_format_of_first_point(annual.plot(), 't = 2014  y = 1.000000')
  File "/tmp/buildd/pandas-0.14.0+git345-g8cd3dd6/debian/tmp/usr/lib/python2.7/dist-packages/pandas/tseries/tests/test_plotting.py", line 135, in check_format_of_first_point
    self.assertEqual(expected_string, ax.format_coord(first_x, first_y))
  File "/tmp/buildd/pandas-0.14.0+git345-g8cd3dd6/debian/tmp/usr/lib/python2.7/dist-packages/pandas/tseries/plotting.py", line 90, in <lambda>
    y))
ValueError: Unknown format code 'f' for object of type 'str'
```

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.3.final.0
python-bits: 32
OS: Linux
OS-release: 3.2.0-4-amd64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: C
LANG: C

pandas: 0.14.0.dev
nose: 1.1.2
Cython: 0.15.1
numpy: 1.6.1
scipy: 0.9.0
statsmodels: 0.5.0
IPython: None
sphinx: 1.1.3
patsy: 0.2.1
scikits.timeseries: None
dateutil: 1.5
pytz: 2012c
bottleneck: None
tables: 2.3.1
numexpr: 1.4.2
matplotlib: 1.1.1rc
openpyxl: 1.7.0
xlrd: 0.6.1
xlwt: 0.7.2
xlsxwriter: None
lxml: None
bs4: 4.0.2
html5lib: 0.90
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: None
pymysql: None
psycopg2: None
```
