Properly test __version__

Comparing int < string always, so '0.7' < 0.8 returns False,
so we have to make it apples to apples (string < string).

String comparison isn't always quite right either, but any future version
will compare > '0.8', so it doesn't matter.
Travis configuration using requirement matrix
Update minimum and maximum revisions

Sphinx>=1.1.3
translate-toolkit>=1.9.0

and for Python 2.5:
Werkzeug<0.9
WTForms<1.0.2