SDL_GL_GetCurrentContext will allow us to replace the weird
implementation in Sdl2Factory.CreateGetCurrentGraphicsContext()
and the latter to disable mouse emulation if we wish to.
Conflicts:
Source/OpenTK/Platform/SDL2/Sdl2.cs
SDL_GL_GetDrawableSize was introduced after 2.0.0, so we need to check for that version before we call this method. Fixes MethodNotFounException on vanilla libsdl2-2.0.0 on linux.
Git commit hashcodes are not compatible with the 16bit integer values found in .Net version numbers. Use the git commit count as a version number instead.