rv10/20: tell decoder to use edge emulation

This removes out-of-edge motion compensation artifacts (easily spotted green
blocks in avplay, gray blocks in transcoding), for example here:
http://samples.libav.org/samples/real/tv_watching_t1.rmSigned-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/rv10.c

@@ -431,6 +431,7 @@ static av_cold int rv10_decode_init(AVCodecContext *avctx)
     s->avctx= avctx;
     s->out_format = FMT_H263;
     s->codec_id= avctx->codec_id;
+    avctx->flags |= CODEC_FLAG_EMU_EDGE;
 
     s->orig_width = s->width  = avctx->coded_width;
     s->orig_height= s->height = avctx->coded_height;