add failing test for ghosted vectors
Allow v=0.0 for ghosted PETSc and Trilinos vectors
Allow v=0.0 for ghosted PETSc and Trilinos vectors
Merge pull request #198 from tjhei/gla_broken_ghost_vec

PETSc and Trilinos vectors with ghost entries can now be reset to zero using = 0.0
Minor doc update.

We had forgotten to update the documentation for the new manifold_id field.
Also a few other touches of TLC.
Merge pull request #199 from bangerth/doc-update-3

Minor doc update for the new manifold_id field.