gc_priv.h (WARN macro): Add "GC warning:" prefix.

	* include/private/gc_priv.h (WARN macro): Add "GC warning:" prefix.
	(GC_large_alloc_warn_interval, GC_large_alloc_warn_suppressed):
	declare.
	* allchblk.c (GC_allchblk_nth): Change text and support reduced
	frequency for blacklist warning message.
	* misc.c (GC_large_alloc_warn_interval,
	GC_large_alloc_warn_suppressed): define.
	(GC_init_inner): Check GC_NO_BLACKLIST_WARNING and
	GC_LARGE_ALLOC_WARN_INTERVAL environment variables.
	* doc/README.environment (GC_NO_BLACKLIST_WARNING): Deprecate.
	(GC_LARGE_ALLOC_WARN_INTERVAL): Add documentation.

	* dyn_load.c (_DYNAMIC): Move declaration to file scope.

From-SVN: r52053