[Thermo] Add getMass/MoleFractionsByName functions with thresholds

This makes it easier to set the composition of a phase based on the composition
of another phase with a different set of species. The threshold argument allows
species with negligible concentrations to be skipped.

Deprecate the unused getMoleFractionsByName function that didn't return a
value.

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@3167 02a645c2-efd0-11dd-984d-ab748d24aa7e
[Cython/Thermo] Add mass/mole_fraction_dict methods

This complements the ability to set the composition using a dict when working
with phases with different sets of species.

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@3168 02a645c2-efd0-11dd-984d-ab748d24aa7e
[SCons] Fix setting 'python_module_loc' with minimal Python module

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@3169 02a645c2-efd0-11dd-984d-ab748d24aa7e