rev-list: add --branches, --tags and --remotes

These flags are already known to rev-parse and have the same meaning.

This patch allows to run gitk as follows:

	gitk --branches --not --remotes

to show only your local work.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rev-list.c

@@ -25,6 +25,9 @@ static const char rev_list_usage[] =
 "    --no-merges\n"
 "    --remove-empty\n"
 "    --all\n"
+"    --branches\n"
+"    --tags\n"
+"    --remotes\n"
 "    --stdin\n"
 "    --quiet\n"
 "  ordering output:\n"