* commit 'c2cb01d4':
  lavf: introduce AVFMT_TS_NEGATIVE

Conflicts:
	libavformat/avformat.h
	libavformat/mux.c
	tests/ref/lavf/asf
	tests/ref/lavf/mkv
	tests/ref/lavf/mpg
	tests/ref/lavf/ts
	tests/ref/seek/lavf-asf
	tests/ref/seek/lavf-mkv
	tests/ref/seek/lavf-mpg
	tests/ref/seek/lavf-ts

This commit does not change the default ts behaviour, such
change will, if its done, be done separately.
Merged-by: Michael Niedermayer <michaelni@gmx.at>