(correct initial timestamps which have AV_NOPTS_VALUE)

sorry, ill rm tests/seek_test ; make ; make seektest from now on

the actual change to the seek test regressions is just adding a small constant
to all timestamps to make the first dts=0 if it was AV_NOPTS_VALUE


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@9949 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b