Make restrict_sr checkbox not tick with multireddit's

Changed line 80 and made + an accepted character in the regex. This means that the Restrict Subreddit checkbox will not be ticked when linking directly to a search using multireddit's.

EG: http://www.reddit.com/r/networking+sysadmin/search?q=UDP+joke
Hi! I think it's a good idea and will get on it when I can (in the next few days) so we can merge this one. Sorry for the late response, I've had a fair amount going on in real life this week.