* glib/gtestutils.h (g_assert_no_error, g_assert_error): Macros to
	assert that a GError is not set, or else is set to a particular
	error.

	* glib/gtestutils.c (g_assertion_message_error): utility for
	those macros

	* glib/tests/keyfile.c:
	* tests/asyncqueue-test.c:
	* tests/bookmarkfile-test.c:
	* tests/convert-test.c:
	* tests/file-test.c: Use g_assert_error/g_assert_no_error

svn path=/trunk/; revision=7555