Don't have SVGImageView store the SVGKImage, nor have an SVGKImage ivar.
Updating OS X's SVGKImageView and subclasses' comments, mainly by changing UIKit calls to AppKit calls.
Make SVGKImage's image property calls throw an assertion instead of logging an error.
Don't have SVGImageView have an SVGKImage ivar on iOS.
Merge branch 'master' into arc

Conflicts:
	Source/AppKit additions/SVGKFastImageView.m
	Source/AppKit additions/SVGKImageView.h
	Source/UIKit additions/SVGKImageView.h