Revert "pst: eyes are normally removable"

confusion continues

This reverts commit 7cab86742fecc65a04e5308260997d0c1fe2457e.
fix cover check for AreaAnimations (broken in d49201fe7)
fix SDL20Video.cpp compilation with gcc/C++11
cmake: added modules for sdl2, sdl2_mixer and glew

first two from Benjamin Eikel and co
last from imageutilities
cmake: added support for building all three versions of SDLVideo

pass -DUSE_SDL2 if you prefer SDL2 on installs with both
pass -DUSE_OPENGL=1 for regular OpenGL, 2 for GLES

tested only the default path, which is still SDL1
cmake: fixed syntax error for opnegl case
SDLVideo: dont disable the OS cursor if the GemRB cursor is set to be disabled

enables better use of SDL2 on non-touchscreen devices by disabling gemrb cursor on those systems. Mostly just want this for testing until the GL driver is fully functional.
in OnMouseUp, don't move after an attempted cast
Merge https://github.com/gemrb/gemrb
GLVideoDriver: few bugfixes (thanks fuzzie). Add an error handling during shader programs creation.