TST fix broken tests (which were using fancy asserts, broke travis py2.6...

... and py3)

Master is not passing travis.

For py2.6: cleared up assertGreater etc. which don't work in py2.6 :(.
For py3: one test is broken in py3 (not sure how to fix):

```
ERROR: test_period_constructor (pandas.tseries.tests.test_period.TestPeriodProperties)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.3_with_system_site_packages/lib/python3.3/site-packages/pandas-0.11.0.dev_4b61349-py3.3-linux-x86_64.egg/pandas/tseries/tests/test_period.py", line 102, in test_period_constructor
    self.assert_(i1 != i4)
  File "/home/travis/virtualenv/python3.3_with_system_site_packages/lib/python3.3/site-packages/pandas-0.11.0.dev_4b61349-py3.3-linux-x86_64.egg/pandas/tseries/period.py", line 132, in __eq__
    raise ValueError("Cannot compare non-conforming periods")
ValueError: Cannot compare non-conforming periods
```