(PhVideoEngine) Fix permanent seek if av_frame_seek returns a future time
(PhSynchronizer) Increase the error bound for synchronisation

With an error bound of 1000, the LTC synchroniser would make the
video jump regularly.
(PhMidiTimeCodeWriter) Do not change time in the middle of a QF sequence
Change the synchronizer spec following the tolerance change
Merge pull request #285 from tlecomte/tlSync

Tl sync
Merge pull request #282 from tlecomte/tlFixAVTimestampConversion

(PhVideoEngine) Fix permanent seek if av_frame_seek returns a future time
Merge pull request #286 from tlecomte/tlSyncErrorBound

sync error bound