Associate bp_stat with bp_location, not breakpoint.

	Associate bp_stat with bp_location, not breakpoint.
	* breakpoint.h (breakpoint_at): Change type
	to bp_location*.
	* breakpoint.c (bpstat_alloc): Take bp_location,
	not breakpoint.
	(bpstat_find_breakpoint): Look at bpstat's location's
	owner, not at bpstat->breakpoint_at.
	(bpstat_find_step_resume_breakpoint): Likewise.
	(bpstat_num): Likewise.
	(print_it_typical): Likewise.
	(print_bp_stop_message): Likewise.
	(watchpoint_check): Likewise.
	(bpstat_what): Likewise.
	(bpstat_get_triggered_catchpoints): Likewise.
	(breakpoint_auto_delete): Likewise.
	(delete_breakpoint): Likewise.
	(bpstat_stop_status): Pass location, not breakpoint,
	to bpstat_alloc.  Look at bpstat's location's
	owner, not at bpstat->breakpoint_at.