Moves a debug statement into debug-only mode.
Fixes broken unit tests from changing foundation images + adds new unit test for bug in images that switch type between CSS and URL.
Adds support for sprite images based on canvas.  This fixes a bug when changing between a sprite and a URL type with the same image that created duplicate elements in the DOM.
Removes two display observers from SC.ImageView and drops undocumented support for setting the value of an image as an array (which was parsed out into a single value for some reason.