Fix for broken events when event targets are SVGElementInstances (in Safari)

[beckiechoi]

W3 states that SVG element be a bit different from the rest of elements. They are a SVGElementInstance, and don't have attributes like nodeType, nodeName, parentNode, etc. A SVGElementInstance instead has a correspondingElement or both a correspondingElement and a correspondingUseElement(for <use/>). Both correspondingElementand correspondingUseElement have all the typical DOM node attributes that you'd expect from other elements.
(ref: http://www.w3.org/TR/SVG/struct.html#InterfaceSVGElementInstance)

Funnily enough, Chrome and Firefox do not follow this "standard", but Safari does.

Currently YUI doesn't have a support for it, making event targets to be null while attempting to wrap a SVGElementInstance into a Y.Node instance; hence this patch.

[yahoocla]

CLA is valid!