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/crcenc.c

@@ -64,4 +64,5 @@ AVOutputFormat ff_crc_muxer = {
     .write_header      = crc_write_header,
     .write_packet      = crc_write_packet,
     .write_trailer     = crc_write_trailer,
+    .flags             = AVFMT_NOTIMESTAMPS,
 };