multiview: PAGEFLIP doesn't require fullscreen (I think)
To be potentially reverted once we get an army of 3-D testers ;)
multiview: add userpref to choose interlace method (UI only)
multiview: implement all interlace methods
Merge branch 'n5' of git://github.com/Alexey-Akishin/blender into Alexey-Akishin-n5
multiview: code cleanup in interlace mode