PR gdb/2250

	PR gdb/2250
	* infrun.c (clear_proceed_status_thread): New function.
	(clear_proceed_status_callback): New function.
	(clear_proceed_status): In all-stop mode, clear per-thread
	proceed status of *all* threads, not only the current.
	(handle_inferior_event): In all-stop mode, if we're stepping
	one thread, but got some inferior event in another thread
	that does not cause GDB to break to the user interface,
	ensure the interrupted stepping operation continues in the
	original thread.
	(currently_stepping): Move thread-related tests to ...
	(currently_stepping_thread): ... this new function.
	(currently_stepping_callback): New function.