Implemented a first version of the motion vector extrapolation error

concealment algorithm. Tested on foreman_cif.yuv only. Some special
cases are still not handled in a good way, for instance when receiving
intra blocks without coefficients.

Change-Id: Ie7bb41855860923b313645dacb3cf70f1e350549

examples/decoder_tmpl.c

@@ -42,6 +42,8 @@ static void die(const char *fmt, ...) {
 
 @DIE_CODEC
 
+@HELPERS
+
 int main(int argc, char **argv) {
     FILE            *infile, *outfile;
     vpx_codec_ctx_t  codec;