Fix problem of restoring the last character after removing value from input.

When user removes value using backspace, the last character goes back because
the timeout is not cleared and server returns query with last letter which
update the input field.
Merge branch 'fix_deletion_of_whole_input' of git://github.com/lucmendelowski/chosen-ajax-addition into lucmendelowski-fix_deletion_of_whole_input
When a user attempts to delete the contents of the search input box, if a request fires off to the server the last character(s) properly get deleted. The last request will get partially ignored by not adding the returned options and not assigning the value of q back to the input box.