revision.c: allow handle_revision_arg() to take other flags

The existing "cant_be_filename" that tells the function that the
caller knows the arg is not a path (hence it does not have to be
checked for absense of the file whose name matches it) is made into
a bit in the flag word.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -2290,7 +2290,7 @@ static void get_object_list(int ac, const char **av)
 			}
 			die("not a rev '%s'", line);
 		}
-		if (handle_revision_arg(line, &revs, flags, 1))
+		if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))
 			die("bad revision '%s'", line);
 	}