_.has checks for object validity before looking for key

Resubmit of pull #1109. When a non-object is passed into _.has, an exception is thrown on the hasOwnProperty. Patch checks that obj is indeed and object and if not, returns false by default.

GitHub for Windows loves to show you that the diff is good (and certainly it is because one's editor is setup to handle spaces/tabs/newlines correctly) but then foobars everything in transit. I should open a ticket on that...