FIX: FulltextFilter did not work and was not usable

This is a fix for #3156
I'm not sure we can do this new API in 3.1. It would be fine to rebase this against master so that it goes into 3.2, but it might be too much of a change for the current version. Can you be 100% certain this will not break any 3.1 existing installs?

Also, don't forget indexes can be specified in one of two ways. An array (as show above) or as a simple text string.

`array('SearchFields' => 'fulltext ("One","Two","Three")')`