Adding CompositeFEMFunction

This and CompositeFunction should be moved to libMesh after a little
testing of the former.
Support ParsedFEMFunction Dirichlet BCs
Handle PARSED_FEM_DIRICHLET case
add dirichlet_fem regression test

At least this is enough to prove that the FEMFunctionBase
DirichletBoundary code works as a plug in for the FunctionBase
DirichletBoundary code.
Delay construction of ParsedFEMFunction

If we just store the strings to be parsed, we don't need a System
argument until we have one in hand.
Use the correct dirichlet_fem input/data files
Try to reinitialize FEMFunction Dirichlet BCs

This isn't giving correct results yet, but (with the proper libMesh
branch) it's at least no longer crashing.
Need EquationSystems to reinit constraints

This whole section of code is hideous and needs libMesh-based
refactoring, but at least it works now.
parsed_fem_dirichlet boundaries now work

So let's get the regression test set down.

This is a horribly understabilized case, but that should be fine for a
regression test.  I don't want to use a finer mesh because I'm afraid
that the Dirichlet<->Neumann transition might be borderline somewhere
and rounding error flipping the sign of u=+/-epsilon might then
trigger a larger change.
Merge pull request #118 from grinsfem/parsed_fem_dirichlet

Parsed fem dirichlet