Notes: See PCJACOBI for point Jacobi preconditioning
This works for AIJ and BAIJ matrices and uses the blocksize provided to the matrix
Uses dense LU factorization with partial pivoting to invert the blocks; if a zero pivot is detected a PETSc error is generated.
Developer Notes: This should support the PCSetErrorIfFailure() flag set to PETSC_TRUE to allow the factorization to continue even after a zero pivot is found resulting in a Nan and hence terminating KSP with a KSP_DIVERGED_NANORIF allowing a nonlinear solver/ODE integrator to recover without stopping the program as currently happens.
Developer Note: Perhaps should provide an option that allows generation of a valid preconditioner even if a block is singular as the PCJACOBI does.