Removed mousenter/mouseleave DOM Event Handling
Removed mousenter/mouseleave DOM Event Handling

Fixes #394

mouseenter/mouseleave are not implemented in Webkit very well, so
reverted to mouseover/mouseout.

mcanthony/openseadragon,LarissaSmith/openseadragon,daverome/openseadragon,avandecreme/openseadragon,shaunstanislaus/openseadragon,shaunstanislaus/openseadragon,daverome/openseadragon,seanich/openseadragon,seanich/openseadragon,ricochet2200/openseadragon,TMUND/openseadragon,rdlester/openseadragon,avandecreme/openseadragon,mcanthony/openseadragon,openseadragon/openseadragon,Iced-Tea/openseadragon,msalsbery/openseadragon,TMUND/openseadragon,lidasong2014/openseadragon,jmnetus/openseadragon,rdlester/openseadragon,jmnetus/openseadragon,lidasong2014/openseadragon,ricochet2200/openseadragon,goofwear/openseadragon,goofwear/openseadragon,LarissaSmith/openseadragon,msalsbery/openseadragon,openseadragon/openseadragon,Iced-Tea/openseadragon