Allow C-c to work in backtrace in more cases

Allow C-c to work in backtrace in more cases

PR cli/17716 notes that it is difficult to C-c (or "q" at a pagination
prompt) while backtracing using a frame filter.  One reason for this
is that many places in py-framefilter.c use RETURN_MASK_ALL in a
try/catch.

This patch changes these spots to use RETURN_MASK_ERROR instead.  This
is safe to do because this entire file is exception safe now.

gdb/ChangeLog
2018-03-26  Tom Tromey  <tom@tromey.com>

	PR cli/17716:
	* python/py-framefilter.c (py_print_type, py_print_value)
	(enumerate_args, py_print_args, gdbpy_apply_frame_filter): Use
	RETURN_MASK_ERROR.