ffplay: extend feedback in case of video changes
ffplay: report video frame changes only in debug mode

In particular, remove distracting message:
"Video frame changed from size:0x0 format:none serial:-1 to ..."
lavf/segment: extend PTS debugging log with -reset_timestamps
ffmpeg: dont allow -flags to override -pass

Fixes Ticket2154

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