APIchanges: Add git version and fix version for avfilter_ref_get_channels().

doc/APIchanges

@@ -18,7 +18,7 @@ API changes, most recent first:
 2013-01-17 - a1a707f - lavf 54.61.100
   Add av_codec_get_tag2().
 
-2012-12-20 - xxxxxxx - lavfi 3.28.100 - avfilter.h
+2012-12-20 - 34de47aa - lavfi 3.29.100 - avfilter.h
   Add AVFilterLink.channels, avfilter_link_get_channels()
   and avfilter_ref_get_channels().