Another commit to increase user friendliness.

o More messages sent to user if material model not built
  and a fortran compiler not found.

o Material database created in the __config__.py file and imported
  from then on.

o Fixed some weird circular imports

o Fixed environment when using subprocess.Popen, subprocess.call
  from permutate or optimize.

o Check prerequisites moved to __config__.py

o python_alternative material model attribute for when a fortran model
  cannot be built.