Make use of the frame stash to detect wider stack cycles.

Make use of the frame stash to detect wider stack cycles.

Tested on x86_64 Fedora 17.

gdb/
2013-11-22  Pedro Alves  <palves@redhat.com>
	    Tom Tromey  <tromey@redhat.com>

	* frame.c (frame_stash_add): Now returns whether a frame with the
	same ID was already known.
	(compute_frame_id): New function, factored out from get_frame_id.
	(get_frame_id): No longer lazilly compute the frame id here.
	(get_prev_frame_if_no_cycle): New function.  Detects wider stack
	cycles.
	(get_prev_frame_1): Use it instead of get_prev_frame_raw directly,
	and checking for stack cycles here.