Fixed bug 2081 - Add name to SDL_Point structure

Dmitry Marakasov

Unlike SDL_Rect (typedef struct SDL_Rect {} SDL_Rect), SDL_Point (typedef struct {} SDL_Point) structure is unnamed. This feels inconsistent and makes it impossible to use forward declaration for SDL_Point, having to include whole SDL_rect.h instead.
Fixed bug 2076 - OpenGL doesn't work with --disable-threads

stepik-777

Thread local storage is used to store current window and current opengl context. OpenGL worked before this changeset: 7596 (45e5c263c096)