Silince UnicodeWarnings in tests

Fixes warning like the following in the test output:
```
/home/travis/virtualenv/python2.7.8/lib/python2.7/site-packages/matplotlib-1.5.x-py2.7-linux-x86_64.egg/matplotlib/text.py:52: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
  if rotation in ('horizontal', None):
```

The changes are somewhat stupid and redundant and the only purpose is to fix the warnings. 
float(None) raises a TypeError