Changes to build with petsc 3.2:
- changing PetscTruth -> PetscBool
- some subroutine interface changes, in particular Vec/MatLoad
- changing petscmg -> petscpcmg for fortran modules and .h header files
Only failing short test was Stokes_Subduction_VK_Case_1b which I adjusted after consultation with Giu+Rhodri.