The grabbed_window field is superfluous now since SDL added the
SDL_GetGrabbedWindow() function, so it can be removed.
DirectFB_SetWindowMouseGrab() is also simplified because SDL handles ungrabbing
any previously grabbed window prior to calling SetWindowMouseGrab() now.
Compile-tested only.
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
