Fix for $.fn.foundationTooltips('destroy')

Previous `destroy` function used the index of the tooltip to re-populate the title attribute of the target element.
This is incorrect because tooltips are added to the dom on mouseenter, therefore each tooltip may not have the same index as the target element (or, indeed the corresponding tooltip may not even be in the DOM).
Merge pull request #1398 from davej/patch-1

Fix for $.fn.foundationTooltips('destroy')