Do not add F77, F90 and FC to PETSc configure line on Darwin, since no Fortran compiler is available.
Merge branch 'master' into hashdist-johannr/petsc-darwin-no-fortran
Add "fortran" parameter

This is a stand in until we get proper Fortran package dependency
support, but should serve most simple cases.
Merge pull request #404 from hashdist/johannr/petsc-darwin-no-fortran

Configure PETSc without F77, F90 and FC when the `fortran` parameter is set to `false`.