Wayland platform: Fix xcomposite backends not to hang after the first GL frame

attach() needs to be called from swapBuffers(), not just once from createSurface().

Change-Id: I8545c1a16179d9e78ae45c0532c89a6298820aa4
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Wayland platform: Do not claim threaded GL support in xcomposite-glx

Change-Id: Ie650bf0b4c243080d8f6173b9e299eb70afc8f90
Reviewed-by: Andy Nichols <andy.nichols@digia.com>