transparent background & better labels position

Partially rewritten to handle transparent background (defining
background color is currently not optional); labels are better
positioned.
Tested only on cairoCanvas.
Merge remote-tracking branch 'gg_upstream/master' into TransparentDrawing_Oct2013
doesn't look completely terrible
that printing is not really necessary
increase the bounding box size
further refinements to the drawing
minor improvements to the aggdraw canvas
more tuning
this is a ways from right, but it is no worse than before
and it has the real advantage of working
Merge branch 'TransparentDrawing_Oct2013'