enable x264 multi-threading

Originally committed as revision 4325 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/x264.c

@@ -154,6 +154,8 @@ X264_init(AVCodecContext *avctx)
     x4->params.i_fps_num = avctx->time_base.den;
     x4->params.i_fps_den = avctx->time_base.num;
 
+    x4->params.i_threads = avctx->thread_count;
+
     x4->enc = x264_encoder_open(&x4->params);
     if(!x4->enc)
         return -1;