Correctly implement M_MXFAST.

Correctly implement M_MXFAST.

	* malloc/malloc.c (struct malloc_state): Replace max_fast with flags
	fields.
	(global_max_fast): New variable.
	(set_max_fast): Change to not require arena parameter and to modify
	global_max_fast.  Change all callers.
	(get_max_fast): New macro.  Use this instead of directly accessing
	now removed max_fast arena member.
	(have_fastchunks): Use flags instead of max_fast.
	(clear_fastchunks): Likewise.
	(set_fastchunks): Likewise.
	(contiguous): Likewise.
	(noncontiguous): Likewise.
	(set_noncontiguous): Likewise.
	(set_contiguous): Likewise.
	(malloc_init_state): Explicitly set FASTCHUNKS_BIT.  Call set_max_fast
	only for main arena.
	* malloc/hooks.c (public_sET_STATe): Adjust set_max_fast use.