crcenc: add flags

AVFMT_NOTIMESTAMPS for crc, as it ignores the timestamps.
AVFMT_VARIABLE_FPS for framecrc, as it prints dts.

Many FATE changes, because avconv is no longer duplicating frames in
those tests.
Also added -vsync 0 for some tests to prevent avconv from dropping
frames until it can be fixed more properly.

libavformat/framecrcenc.c

@@ -40,4 +40,5 @@ AVOutputFormat ff_framecrc_muxer = {
     .audio_codec       = CODEC_ID_PCM_S16LE,
     .video_codec       = CODEC_ID_RAWVIDEO,
     .write_packet      = framecrc_write_packet,
+    .flags             = AVFMT_VARIABLE_FPS,
 };