Partial fix for memory leak. Not entirely sure why this works, but it seems not nulling inaccessible private members during dispose can cause a leak - surely if the parent objects were being orphaned, that would mean anything only they reference would also be ellegible for GC? Looks like I may need to read up on the flash player GC again . . .
Merge remote-tracking branch 'origin/master'

Conflicts:
	extension/bin/Starling-Extension-Graphics.swc