Fix text rotation with canvas

The text entity was directly using it's x/y coordinates to draw on the canvas.  To account for rotation, it needs to use the coordinates passed by the draw event.

As reported on the [forums](https://groups.google.com/forum/?fromgroups=#!topic/craftyjs/ZLefsBR6zFA).

I manually checked that canvas text appears correctly with this patch.  But the effects are purely visual, so unfortunately there's no easy way to add a test for the correct behavior.  I think there are tools that let you test canvas rendering, so maybe we should investigate those!  :)