Making MOOSE and modules compile when libmesh is configured --with-dof-id-bytes=8.

Refs #4321.
Add test harness option to restrict tests to specific
--with-dof-id-bytes configurations.

Restricting the aux_nonlinear_solution_from_xdr to only run when
libmesh has been configured with 4-byte dof ids.

Refs #4321.
Fixing 32/64bit conversion warnings found with -Wconversion

Refs #4321.