Add support for interlaced polarized 3d screens
Add (experimental) support for topbottom as well as sidebyside 3d mode
Merge commit '09970b7' into merge3

Conflicts:
	src/CMakeLists.txt
	src/clientmap.h
	src/content_cao.cpp
	src/defaultsettings.cpp
	src/game.cpp
	src/localplayer.h