Previously, ownership of the pixmaps that we are using for double buffering was
a little weird. The pixmap belonged to the drawin/titlebar, but the
corresponding cairo surface was owned by the drawable. Clean this up by moving
the pixmap to the drawable.
This cleans up lots of ugly code and also fixes a crash: When a drawable was
garbage collected before its drawin, drawin_wipe() would crash accessing the
drawable. This was needed to make it forget about the cairo surface we gave to
it for the pixmap that is being destroyed.
By moving the pixmap to the drawable, this whole issues goes away.
Signed-off-by: Uli Schlachter <psychon@znc.in>
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