Adding support for petsc-3.4 as a solver.
This involves fairly minimal changes from the code used for
petsc-3.3. This doesn't attempt to use any new features
introduced in 3.4 but tries to ensure the same behaviour as
runs with earlier petsc versions.
Adding preliminary support for petsc-3.5.
Code compiles and simple tests seems to work fine, but a lot has changed
between 3.4 and 3.5 and it's not clear exactly how to update things in
all places. Therefore this should be treated as incomplete/untested.
Updated configure/configure.ac to enable MUMPS if at least one of metis/parmetis and ptscotch is available, instead of requiring both
Added -fpermissive to CXXFLAGS in src/invert/laplace/impls/petsc to allow strcpy to write to a KSPType {aka const char*}. Also removed -g CXXFLAGS (which are unneeded as the --with-debug option to configure does that).