Canvas update

These commits impact Canvas functions affecting mainly ie6/7/8, merge if support for these is maintained. Two commits relate to https://github.com/pyjs/pyjs/pull/788, changed HTML5Canvas to correct translator failure and added necessary methods to HTML5CanvasImplIE6. Stumbled across errors in transform method of GWTCanvasImplIE6, changed to make it functional and for proper transformation. Following changes, programs using these functions ran properly in firefox v21 and ie6.