API changes for PETSc compatibility since release-3.3.0

Guys, take a look at this patch, which restores compatibility with PETSc since release-3.3.0 in preparation for release-3.4.0, hopefully, in a backward-compatible way. I did some limited testing by building against petsc-3.3 and petsc-3.2 and running miscellaneous/ex7, which exercises DMlibMesh to serve up vector bounds to a VI solver (there may be some regression on the PETSc side there, but the libMesh code seems to be fine).

There will probably be at least one more such pull request before petsc-3.4.0 release.
That patch will fix DMlibMeshCreateXXXDecomposition() for better interaction with PC(G)ASM and PCFIELDSPLIT -- those are effectively turned off at the moment and I want to do some substantial refactoring there before another commit.