While here, update to cogl to 1.20.0
Cogl 1.20.0 2015-03-23
List of changes since Cogl 1.18.2
Support for "quad buffer" based stereo rendering
Support for Mir window system
A number of updates for the Wayland support
Improved vblank sync when using glXWaitForMSC
Many thanks to:
Marco Trevisan (Trevino)
Owen W. Taylor
Robert Bragg
Rui Matos
Adel Gadllah
Chris Wilson
Necdet Yuel
Sebastian Rasmussen
Seong-ho Cho
Ting-Wei Lan
