[binutils-gdb] Use gdbpy_ref in python.c

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 59876f8f9f32081b2831aed83a03a815e8d85a97 ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 59876f8f9f32081b2831aed83a03a815e8d85a97

Use gdbpy_ref in python.c

This changes more places in python.c to use gdbpy_ref.

Additionally, previously gdbpy_apply_type_printers would return
EXT_LANG_RC_ERROR if a type printer returned None.  However, that
doesn't seem correct to me; this patch changes it to return
EXT_LANG_RC_NOP in this case.

2017-01-10  Tom Tromey  <tom@tromey.com>

	* python/python.c (eval_python_command, gdbpy_decode_line)
	(gdbpy_run_events, gdbpy_start_type_printers)
	(gdbpy_apply_type_printers): Use gdbpy_ref.