non-opengl backend rendering issues

[Antoine Martin]

Found by testing for #1658 with:

• wayland as vfb
• a patch to return True from check_randr_sizes
• opengl=no

With python2, the rendering is broken, with python3 the client crashes!

[Antoine Martin]

r19645 adds better debug logging.
The problem seems to come from relative vs absolute coordinates: some methods call queue_draw with relative coordinates, others expect it to honour absolute coordinates and repaint the whole window, including the padding area..

[Antoine Martin]

Large fix in r19647, also fixes the crashes with python3. (looks like cairo / python3 doesn't do enough validation and just crashes... python2 just renders junk?)
queue_draw is part of the GTK API, we should always use absolute window coordinates there.

Other related changesets:

• r19649: mmap fix for python2 cairo backend
• r19645 + r19646 + r19648: debug logging improvements

[totaamwin32]

r19647 caused a regression: ticket:1339#comment:35.

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/1874