
Enable double buffering for panes created with :DOUBLE-BUFFERING T only.
Gsharp already uses this method.

	* Backends/gtkairo/port.lisp (*DOUBLE-BUFFERING-P*): Removed.
	(MIRROR-DRAWABLE): Use PANE-DOUBLE-BUFFERING, not *d-b-p*.

quek/mcclim,informatimago/mcclim,informatimago/mcclim,quek/mcclim