COMP: Added KWSYS_CXX_HAS_CSTDDEF try-compile to KWSys to provide kwsys/cstddef header (to get size_t for hash_fun.hxx).

ENH: Adding SGI hash_map and hash_set implementation ported from STL to KWSys.  This also adds try-compiles for KWSYS_STL_HAS_ALLOCATOR_REBIND, KWSYS_CXX_HAS_FULL_SPECIALIZATION, KWSYS_CXX_HAS_MEMBER_TEMPLATES, and KWSYS_CXX_HAS_NULL_TEMPLATE_ARGS.