t0040,t1502: Demonstrate parse_options bugs

When the option spec contains no switches or only hidden switches,
parse_options will emit an extra blank line at the end of help output so
that the help text will end in two blank lines instead of one.

When parse_options produces internal help output after an error has
occurred it will emit blank lines within the usage string to stdout
instead of stderr.

Update t/helper/test-parse-options.c to have a description body in the
usage string to exercise this second bug and mark tests as failing in
t0040.

Add tests to t1502 to demonstrate both of these problems.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-parse-options.c

@@ -99,6 +99,8 @@ int cmd_main(int argc, const char **argv)
 	const char *prefix = "prefix/";
 	const char *usage[] = {
 		"test-parse-options <options>",
+		"",
+		"A helper function for the parse-options API.",
 		NULL
 	};
 	struct string_list expect = STRING_LIST_INIT_NODUP;