Update FOF to 2.1.rc4

This only updates FOF to 2.1.rc4, including bug fixes affecting display issues under Joomla! 3.2.

Summary of changes:

+ Added DTD for XML forms under documentation/form.dtd
+ Add Joomla formatter for FOFLess
+ 'btn' class assigned to buttons of fieldsearchable by default (adheres to Joomla! 3 styling guidelines)
+ Using icons for fieldsearchable's search/reset buttons
~ Update to lessc 0.3.9
~ FOF table caching now respects Joomla! caching options (is it enabled, cache handler and cache lifetime).
# Error when deleting entry of FOFTable which is using assets
# jquery.ui.tooltip.js in AkeebaStrapper::jQueryUI() breaks Joomla 3 tooltip
# JHtml::_('behavior.multiselect') must be loaded in Joomla 2.5 and for FOFRenderJoomla
# Unable to add component-specific behaviours to models
# Fix loadTemplate behaviour on J3+
# When the table cache reports a table as non-existent (e.g. the server failed to reply to SHOW TABLES) you had to clean the cache to see the table in FOF
# JFormField changes in Joomla! 3.2 Beta 1 broke FOF form fields