Fixed bug 1744 - DirectFB video and renderer API is not updated

tomaszewski.p

Recent changes in SDL_sysrenderer.h and SDL_sysvideo.h had no impact on directfb backend.

Attached patch:
- updates interface,
- resolves uninitialized variable reading,
- changes logging tio use SDL_Log API,
- updates configure to use DIRECTFBCONFIG variable instead direct call to directfb-config.