parseopt: wrap rev-parse --parseopt usage for eval consumption

9c7304e (print the usage string on stdout instead of stderr,
2010-05-17) broke rev-parse --parseopt: when run with -h, the usage
notice on stdout ended up in the shell eval.

Wrap the usage in a cat <<\EOF ... EOF block when printing to stdout.
I do not expect any usage lines to ever start with EOF so this
shouldn't be an undue burden.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-parse.c

@@ -408,7 +408,8 @@ static int cmd_parseopt(int argc, const char **argv, const char *prefix)
 	memset(opts + onb, 0, sizeof(opts[onb]));
 	argc = parse_options(argc, argv, prefix, opts, usage,
 			keep_dashdash ? PARSE_OPT_KEEP_DASHDASH : 0 |
-			stop_at_non_option ? PARSE_OPT_STOP_AT_NON_OPTION : 0);
+			stop_at_non_option ? PARSE_OPT_STOP_AT_NON_OPTION : 0 |
+			PARSE_OPT_SHELL_EVAL);
 
 	strbuf_addf(&parsed, " --");
 	sq_quote_argv(&parsed, argv, 0);