Override sorting locale in rebuild_libmesh_SOURCES

My locale wasn't doing POSIX sorting and the result was unnecessarily
large diffs when changing libmesh_SOURCES
Factor SyncNodalPositions out of that anonymous namespace so we can
use it elsewhere in the library.
Add a non-const getter for _mesh_sys
get_physics()/get_qoi() const/non-const getters
Better accessors for moving mesh problems
Fix moving mesh code parallelism, regressions
Merge branch 'master' of ssh://github.com/libMesh/libmesh