Fix problems for older ffmpeg versions

Fix the following issues when building against older ffmpeg versions

- the call to avcodec_free_context exceptions as avformat_close_input
  already performs cleanup of the AVCodecContext, so link the calling of
  avcodec_free_context in the close method of k9avidecode.cpp to the
  version of libavformat in which codecpar appeared rather than when
  avcodec_free_context appeared.
- avcodec_decode_video2 was deprecated in libavcodec 57.106.100, not
  57.12.100, so the version has been corrected.

Signed-off-by: aneejit1 <aneejit1@gmail.com>

k9author/k9avidecode.cpp

@@ -216,7 +216,7 @@ void k9AviDecode::readFrame(double _seconds) {
         // Is this a packet from the video stream?
         if (packet->stream_index==m_videoStream) {
             // Decode video frame
-#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(57, 37, 100)
+#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(57, 106, 100)
             int ret = avcodec_receive_frame(m_CodecCtx, m_Frame);
             if (ret == 0)
                 frameFinished = 1;
@@ -300,7 +300,7 @@ void k9AviDecode::close() {
         av_close_input_file(m_FormatCtx);
 #endif
 
-#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(55, 63, 100)
+#if LIBAVFORMAT_VERSION_INT >= AV_VERSION_INT(57, 33, 100)
         avcodec_free_context(&m_CodecCtx);
 #endif