Test compiler features using our devel flags

It turns out that not just user-provided flags can affect system
features, so can libMesh-provided flags.

Testing with our devel flags works around a gcc 3.4 bug wherein
xmmintrin.h isn't compilable with the -pedantic option.
Fixes for petsc-without-MPI

With our new multi-communicator-capable code we've also got a bunch
more places where we pass libMesh::Parallel::communicator objects in
to PETSc arguments expecting an MPI_Comm, which they typedef to
represent int.  The most robust fix is for us to match that.
Add string_to_enum specialization

We can convert from strings to SolverTypes and back now.
Use enum_to_string when printing SolverTypes
Disable a few examples with Eigen/Trilinos

One of these days we ought to look into *why* those solvers are
failing on these problems...
Missed a enum_to_string specialization
And a string_to_enum specialization
Don't forget the #include for that enum
Examples must init libMesh *before* using our APIs
Use recursive $(MAKE) in "make doc"
Propagate Makefile.am change through bootstrap