vcl: Add method to swap buffers after painting window

Change-Id: Icdf691e7e9e83d039e33d2095270290dc31f2efa
vcl: Get visual info for window from GLX when needed

Change-Id: Id8cea87391835694e20aa703b7fdb3f13434d47b
vcl: Add list of contexts sharing the same display list

Change-Id: Ib1bca0aaaf41140d6b9a17378094b0f20e469ebd