Give error for unsupported petsc 3.6.0 case.
Give error for unsupported petsc 3.6.0 case.

If using nullspaces for solves where we have a different preconditioner
matrix, we don't support petsc 3.6.0 (referred to by petsc as v3.6).
3.6.1 and higher and <=3.5 should be supported.

iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,rjferrier/fluidity,rjferrier/fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,jrper/fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jrper/fluidity,rjferrier/fluidity