Fixes #2367, closes #2467 - Use the check when using delegation for mouseenter.

Since 1.4.2 the native mouseenter/mouseleave events are used, when available
(Firefox, IE). For delegation however, it should has to use mouseover/mouseout
because it should still fire each time an element is entered or left so it can
check if it matches the selector.

thanks @luisateixeira for the research/fix