AkhIL mentioned on IRC that bitmaps weren't working with 'straight onto' blending...

AkhIL mentioned on IRC that bitmaps weren't working with 'straight onto' blending.  It turned out that the clone-and-encapsulate we do to get straight blending to work was failing because clone() needs to know the path to the file that the canvas is stored in to calculate the relative path to the image file, and the optimized copy of the canvas tree didn't have that information.  Now it does.

git-svn-id: http://svn.voria.com/code@1526 1f10aa63-cdf2-0310-b900-c93c546f37ac