ext/: Fix various compiler warnings that reveal potential bugs.

ext/: Fix various compiler warnings that reveal potential bugs.

Original commit message from CVS:
2007-01-04  Julien MOUTTE  <julien@moutte.net>

* ext/directfb/dfbvideosink.c:
(gst_dfbvideosink_navigation_send_event),
(gst_dfbvideosink_get_type):
* ext/sdl/sdlaudiosink.c: (gst_sdlaudio_sink_open):
* ext/sdl/sdlvideosink.c: (gst_sdlvideosink_setcaps),
(gst_sdlvideosink_show_frame),
(gst_sdlvideosink_navigation_send_event):
* ext/sdl/sdlvideosink.h: Fix various compiler warnings that
reveal potential bugs.