PR python/15620, PR python/18620 - breakpoint events in Python

This patch adds some breakpoint events to Python.  In particular,
there is a creation event that is emitted when a breakpoint is
created; a modification event that is emitted when a breakpoint
changes somehow; and a deletion event that is emitted when a
breakpoint is deleted.

In this patch, the event's payload is the breakpoint itself.  I
considered making a new event type to hold the breakpoint, but I
didn't see a need.  Still, I thought I would mention this as a spot
where some other choice is possible.

Built and regtested on x86-64 Fedora 23.

2016-07-13  Tom Tromey  <tom@tromey.com>

	PR python/15620, PR python/18620:
	* python/py-evts.c (gdbpy_initialize_py_events): Call
	add_new_registry for new events.
	* python/py-events.h (events_object) <breakpoint_created,
	breakpoint_deleted, breakpoint_modified>: New fields.
	* python/py-breakpoint.c (gdbpy_breakpoint_created): Emit the
	breakpoint changed event.
	(gdbpy_breakpoint_deleted): Emit the breakpoint deleted event.
	(gdbpy_breakpoint_modified): New function.
	(gdbpy_initialize_breakpoints): Attach to the breakpoint modified
	observer.

2016-07-13  Tom Tromey  <tom@tromey.com>

	PR python/15620, PR python/18620:
	* python.texi (Events In Python): Document new breakpoint events.

2016-07-13  Tom Tromey  <tom@tromey.com>

	PR python/15620, PR python/18620:
	* gdb.python/py-breakpoint.exp (connect_event, check_last_event)
	(test_bkpt_events): New procs.

gdb/python/py-events.h

@@ -50,6 +50,9 @@ typedef struct
   eventregistry_object *inferior_call;
   eventregistry_object *memory_changed;
   eventregistry_object *register_changed;
+  eventregistry_object *breakpoint_created;
+  eventregistry_object *breakpoint_deleted;
+  eventregistry_object *breakpoint_modified;
 
   PyObject *module;