show-branch: mark --reflog option as NONEG

Running "git show-branch --no-reflog" will behave as if "--reflog" was
given with no options, which makes no sense.

In theory this option might be used to cancel an earlier "--reflog"
option, but the semantics are not clear. Let's punt on it and just
disallow the broken option.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/show-branch.c

@@ -674,7 +674,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 		{ OPTION_CALLBACK, 'g', "reflog", &reflog_base, N_("<n>[,<base>]"),
 			    N_("show <n> most recent ref-log entries starting at "
 			       "base"),
-			    PARSE_OPT_OPTARG,
+			    PARSE_OPT_OPTARG | PARSE_OPT_NONEG,
 			    parse_reflog_param },
 		OPT_END()
 	};