libmesh_cast_foo -> cast_foo

This gives our cast methods names which are no longer redundant with
their namespace.

The old names remain for backwards compatibility but are marked
deprecated
libmesh_cast_foo -> cast_foo in source

libMesh library files no longer use the deprecated cast functions
libmesh_cast_foo -> cast_foo in examples
Define libmesh_deprecated before new use
Fix typo
Merge pull request #319 from libMesh/cast_foo

libmesh_cast_foo -> cast_foo