This allows the code to modify packets (which are non-mutable due to reference counting)
by copying them without having to also copy the packet payload.
* Avoid extracting persistent data (such as video width*height) from
received data if we suspect that an error has occured (MPEG-TS TEI or
continuity counter errors).
* Add src/plumbing/tsfix.[ch]: Streaming code that fixes up missing
timestamps and normalize timecode to start at 0.
* Move PTS estimation code and timestamp normalization out from central
parse code. Subscribers that really needs it should use tsfix plumbing
instead.
* Let DVR code use tsfix plumbing.
* Don't send "pts" and "dts" over HTSP if timestamps are missing.
