In order that people can use formats like #D in #() in the status line

and not have to wait for an update when they change pane, we allow
commands to run more than once a second if the expanded form
changes. Unfortunately this can mean them being run far too often
(pretty much continually) when multiple clients exist, because some
formats (including #D) will always differ between clients.

To avoid this, give each client its own tree of jobs which means that
the same command will be different instances for each client - similar
to how we have the tag to separate commands for different panes.

GitHub issue 889; test case reported by Paul Johnson.

cmd-pipe-pane.c

@@ -90,7 +90,7 @@ cmd_pipe_pane_exec(struct cmd *self, struct cmdq_item *item)
 	}
 
 	/* Expand the command. */
-	ft = format_create(item, FORMAT_NONE, 0);
+	ft = format_create(item->client, item, FORMAT_NONE, 0);
 	format_defaults(ft, c, s, wl, wp);
 	cmd = format_expand_time(ft, args->argv[0], time(NULL));
 	format_free(ft);