Introduce two new logging functions av_hex_dump_log() and av_pkt_dump_log()

which use av_log() for logging instead of fprintf().

Originally committed as revision 8339 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -1878,7 +1878,7 @@ static int av_encode(AVFormatContext **output_files,
         }
 
         if (do_pkt_dump) {
-            av_pkt_dump(stdout, &pkt, do_hex_dump);
+            av_pkt_dump_log(NULL, AV_LOG_DEBUG, &pkt, do_hex_dump);
         }
         /* the following test is needed in case new streams appear
            dynamically in stream : we ignore them */