Add DofMap::(un)stash_dof_constraints()

Adjoint-based sensitivity calculations can require us to calculate
residuals without applying constraints, and this seems to be the least
modularity-defiling way to let us turn them off and back on quickly.
adjoint_qoi_sensitivity bugfix for adjoint BCs

With heterogeneous adjoint BCs we can't constrain the residual vector
and still expect to accurately calculate adjoint-weighted residuals
with a dot product.
Fix lift_func errors in adjoint qoi sensitivity

Choosing the right BCs and not making a sign error might be helpful...
Use API properly

enforce_constraints_exactly took a pointer to allow for a default
NULL; but enforce_adjoint_constraints exactly takes a reference...
has_heterogenous_adjoint_constraint changes

New method has_heterogenous_adjoint_constraints tests for any such
constraints.

Old method has_heterogenous_adjoint_constraint new returns the
constraint rhs Number rather than bool; this should be semantically
backward-compatible with the old system unless someone was manually
setting a zero constraint and expecting that to count as heterogenous.
Integrate regularized flux QoIs in FEMSystem
FEMSystem integration of heterogeneous qoi_deriv

This is consistent with the new assemble_qoi behavior
Selectively apply liftfunc and constraints

We need the liftfunc terms to be left out of the RHS for adjoint
solves; we need QoI derivative vectors to be left unconstrained when
using them for dot products in sensitivity calculations.
Fix a bug Vikram caught in FEMSystem qoi derivs
Test the return value of FunctionParser::Parse()
Fix unused variable warning when !LIBMESH_HAVE_MPI
Fix GCC 4.8 'possibly uninitialized' variable warning.
Fix configure test for unordered_set.

This had no chance of passing because it was not valid C++.
Use quadrigraph '@%:@' for literal hash '#' characters in m4 scripts.

This helps prevent syntax highlighting editors from displaying these
lines as comments.  Also reformatted some of the autoconf tests
slightly to make the easier to read.
Ran bootstrap.
Some opt-mode error checking in Parsed*Function

Leaving these tests on shouldn't be too much overhead relative to
the parsing process that already takes place in these constructors.

And since the whole point of parsed functions is to allow users to
change the string contents at run time, there's no way for us to
guarantee that those strings will be valid the way we can (attempt to)
make such guarantees about other assertions.
Merge pull request #394 from libMesh/parsed_fem_func_check

More tests when constructing Parsed*Function
Fix configure test for unordered_set.

This had no chance of passing because it was not valid C++.
Remove old references to aclocal.m4 in comments.

aclocal.m4 is now generated by automake...

Refs #386.
Fix AC_MSG_RESULT typo.