Fix for #274
Make the Bundler warning less scary and more friendly
It's true the message may be a bit too obvious now -- if you're not happy about it, let me know and I'll see what I can do to edit it down.
Oops it breaks the specs badly :( http://travis-ci.org/#!/guard/guard/builds/1072250
Whoops! Sorry. I should know better than to not run the tests. If you pull the branch again, I've fixed them.