gdb/py: convert debug logging in py-unwind to use new scheme

gdb/py: convert debug logging in py-unwind to use new scheme

Converts the debug print out in python/py-unwind.c to use the new
debug printing scheme.  I have also modified what is printed in a few
places, for example, rather than printing frame pointers, I now print
the frame level, this matches what we do in the general 'set debug
frame' tracing, and is usually more helpful (I think).

I also added a couple of ENTER/EXIT scope printers.

gdb/ChangeLog:

	* python/py-unwind.c (pyuw_debug): Convert to bool.
	(show_pyuw_debug): New function.
	(pyuw_debug_printf): Define.
	(PYUW_SCOPED_DEBUG_ENTER_EXIT): Define.
	(pyuw_this_id): Convert to new debug print macros.
	(pyuw_prev_register): Likewise.
	(pyuw_sniffer): Likewise.
	(pyuw_dealloc_cache): Likewise.
	(_initialize_py_unwind): Update now pyuw_debug is a bool, and add
	show function when registering.