Reduced sleep while waiting for a frame in transcode.

 It vastly improves CPU usage but it does not fix the underlaying problem
of using sleep instead of a signal.

manually cherry-picked by jb@videolan.org

modules/stream_out/transcode.c

@@ -2158,7 +2158,7 @@ static picture_t *video_new_buffer( vlc_object_t *p_this, picture_t **pp_ring,
         {
             /* Encoder still has stuff to encode, wait to clear-up the list */
             while( p_sys->i_first_pic == i_first_pic )
-                msleep( 100000 );
+                msleep( 5000 );
         }
 
         /* Find an empty space in the picture ring buffer */