Preserve compatibility with ffmpeg 2.8 for rc-min-rate option.

Index: gst-libav-1.6.3/ext/libav/gstavcfg.c
===================================================================
--- gst-libav-1.6.3.orig/ext/libav/gstavcfg.c
+++ gst-libav-1.6.3/ext/libav/gstavcfg.c
@@ -524,9 +524,15 @@ gst_ffmpeg_cfg_init (void)
 #endif
   gst_ffmpeg_add_pspec (pspec, config.rc_max_rate, FALSE, mpeg, NULL);
 
+#if LIBAVCODEC_VERSION_INT < AV_VERSION_INT (57, 3, 0)
+  pspec = g_param_spec_int ("rc-min-rate", "Ratecontrol Minimum Bitrate",
+      "Ratecontrol Minimum Bitrate", 0, G_MAXINT, 0,
+      G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
+#else
   pspec = g_param_spec_int64 ("rc-min-rate", "Ratecontrol Minimum Bitrate",
       "Ratecontrol Minimum Bitrate", 0, G_MAXINT64, 0,
       G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
+#endif
   gst_ffmpeg_add_pspec (pspec, config.rc_min_rate, FALSE, mpeg, NULL);
 
   pspec =