gdb/

gdb/
	* infrun.c (infrun_thread_thread_exit): New.
	(_initialize_infrun): Attach it to the thread_exit observer.
	* thread.c (delete_thread_1): Always call the observer, passing it
	the silent flag.
	* mi/mi-interp.c (mi_thread_exit): Add "silent" parameter.  If
	SILENT, return immediately.

gdb/doc/
	* observer.texi (thread_exit): Add "silent" parameter.