v.get_stencil_width() == 0 if v has no ghosts.
thksmooth and schoofs_theta diagnostics don't need ghosts.
Cleanup.
Add IceModelVec::get_dm()

Some PETSc calls (such as DMDAGlobalToNaturalBegin(DM da, Vec
g,InsertMode mode,Vec l)) require that arguments "Vec g" and "Vec l" use
the same DM, or maybe at least that "DM da" was the one used to create
"Vec l". This IceModelVec method makes it easier to ensure this holds.
Commit ff45421 broke IcebergRemover. This should fix it.
Fix a typo introduced in 6f1fe04.

(V does not need ghosts, W does.)