Use LooseVersion from distutils to check Cython version in order to handle non-integers in the version string.
Minimal tests to cover using distutils.version.LooseVersion for pyrex.
Credit Andrew for the fix.
(vila) Use LooseVersion from distutils to check Pyrex/Cython version in
 order to handle non-integers in the version string. (Andrew Starr-Bochicchio)