Set AVFMT_TS_NONSTRICT for framecrc muxer.

Since it is set for e.g. webm muxer we should make it possible
to test such streams with framecrc, too.
Though the primary reason is that this allows the H.264 tests
to not run into this check when fixing raw video encode to
pass pts values on.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
