[Scons] Fix build order dependencies for python modules

git-svn-id: https://cantera.googlecode.com/svn/cantera/branches/2.1@2517 02a645c2-efd0-11dd-984d-ab748d24aa7e
[Cython] Fix syntax errors in MixMaster for Python 3

Backticks are not allowed in Python 3 (equivalent to repr)

git-svn-id: https://cantera.googlecode.com/svn/cantera/branches/2.1@2518 02a645c2-efd0-11dd-984d-ab748d24aa7e