avformat/segment: Support cutting at clocktime

Signed-off-by: Deti fliegl <fliegl@baycom.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/segment: simplify localtime* use

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/vmdvideo: remove unneeded include

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>