gdb/python: allow for catchpoint type breakpoints in python

gdb/python: allow for catchpoint type breakpoints in python

This commit adds initial support for catchpoints to the python
breakpoint API.

This commit adds a BP_CATCHPOINT constant which corresponds to
GDB's internal bp_catchpoint.  The new constant is documented in the
manual.

The user can't create breakpoints with type BP_CATCHPOINT after this
commit, but breakpoints that already exist, obtained with the
`gdb.breakpoints` function, can now have this type.  Additionally,
when a stop event is reported for hitting a catchpoint, GDB will now
report a BreakpointEvent with the attached breakpoint being of type
BP_CATCHPOINT - previously GDB would report a generic StopEvent in
this situation.

gdb/ChangeLog:

	* NEWS: Mention Python BP_CATCHPOINT feature.
	* python/py-breakpoint.c (pybp_codes): Add bp_catchpoint support.
	(bppy_init): Likewise.
	(gdbpy_breakpoint_created): Likewise.

gdb/doc/ChangeLog:

	* python.texinfo (Breakpoints In Python): Add BP_CATCHPOINT
	description.

gdb/testsuite/ChangeLog:

	* gdb.python/py-breakpoint.c (do_throw): New function.
	(main): Call do_throw.
	* gdb.python/py-breakpoint.exp (test_catchpoints): New proc.