Align behavior of xmethod commands with that of pretty-printer commands.

Align behavior of xmethod commands with that of pretty-printer commands.

Currently, the xmethod commands lookup xmethod matchers in the current
progspace even if the locus regular expression matches the progspace's
filename.  Pretty printer commands do not match the current progspace's
filename.

gdb/

	* python/lib/gdb/command/xmethods.py
	(get_method_matchers_in_loci):  Lookup xmethod matchers in the
	current progspace only if the string "progspace" matches LOCUS_RE.

gdb/testsuite

	* gdb.python/py-xmethods.exp: Use "progspace" instead of the
	progspace's filename in 'info', 'enable' and 'disable' command
	tests.