#2031 - Add class_exists() before method_exists() if class existence is unknown.
- fixed all instances of this in core code
- deleted previous Zend Guard Loader workaround in MY_Kohana.php
- updated Bootstrap.php to reflect deleted MY_Kohana.php
Remove deprecated $.browser call.  Fixes #2029.
#2018 - Make ui.init.js thumbnail hover effect more robust.
- changed thumbnail hover effect to store its original height on mouseenter, then return to it on mouseleave.
- removed previous routine which depended on the height of its siblings and was incompatible with some IE versions.