linux_threads.c (return_free_lists): Clear fl[i] unconditionally.

linux_threads.c (return_free_lists): Clear fl[i] unconditionally.

	* linux_threads.c (return_free_lists): Clear fl[i] unconditionally.
	(GC_local_gcj_malloc): Add assertion.
	(start_mark_threads): Fix abort message.
	* mark.c (GC_mark_from): Generalize assertion.
	* reclaim.c (GC_clear_fl_links): New function.
	(GC_start_reclaim): Must clear some freelist links.
	* include/private/specific.h, specific.c: Add assertions.
	Safer definition for INVALID_QTID, quick_thread_id.  Fix/add comments.
	Rearrange tse fields.

From-SVN: r51582