vector_as_adjoint changes

Change name to vector_is_adjoint; anybody using this API probably
should be paying attention to this commit anyways.

Fix default vector behavior: handle projections with primal rather
than adjoint BCs.  I'm not sure why this took so long to trigger a
regression anywhere; are we doing a redundant constraint application
with the correct rhs after projections?
Merge pull request #358 from libMesh/set_adjoint_fix

vector_as_adjoint changes
Add semilocal_elements iterators
Slight adjoints_ex3 generalization
Compute constraints on semilocal elements