Added GC_LONG_REFS_NOT_NEEDED ifdefs to exclude long link

Added GC_LONG_REFS_NOT_NEEDED ifdefs to exclude long link
functionality and other minor changes.

* finalize.c (GC_push_finalizer_structures,
GC_register_long_link, GC_unregister_long_link,
GC_move_long_link, GC_finalize): GC_LONG_REFS_NOT_NEEDED ifdefs to
exclude long link functionality.
* finalize.c (GC_dump_finalization_links,
GC_register_disappearing_link_inner,
GC_move_disappearing_link_inner): Changed from GC_INLINE to STATIC
function declaration.
* include/gc.h: use 2 spaces as a sentence delimiter in comment
added in previous commit.