Filter limit bug

While testing a new filter, I discovered that the limit filter had a problem.

If !limit (not limit) was used, nothing was ever returned. The code indicates that it should return [limit] amount of tiddlers from the end of the tiddler results, rather than the beginning. 

I removed the faulty parameter in limit.js and added a jasmin test to verify it works correctly and am submitting a pull request.

David Johnston
@Brennall