[SCons] Check Cython version for Python 2.x

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@2483 02a645c2-efd0-11dd-984d-ab748d24aa7e
[SCons] Check Cython version for Python 3.x

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@2484 02a645c2-efd0-11dd-984d-ab748d24aa7e
[Cython] Fix Python 2.6 compatibility issues with sys.version_info

The "major" attribute is a new feature in Python 2.7.

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@2485 02a645c2-efd0-11dd-984d-ab748d24aa7e