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

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 ``correspondingElement``and ``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.