Modify all codecs to report their supported input and output sample format(s).

Originally committed as revision 14482 to svn://svn.ffmpeg.org/ffmpeg/trunk
diff --git a/libavcodec/mpc7.c b/libavcodec/mpc7.c
index a975db3..565b858 100644
--- a/libavcodec/mpc7.c
+++ b/libavcodec/mpc7.c
@@ -108,6 +108,7 @@
         }
     }
     vlc_initialized = 1;
+    avctx->sample_fmt = SAMPLE_FMT_S16;
     return 0;
 }