* modules/mux/mpeg/pes.c: Copy the flags of the data buffer to the PES
buffer.
* modules/mux/mpeg/ts.c:
- rename the caching= option into shaping= since it more adequately
describes what it does
- new use-key-frames option, if enabled then shaping= will be a
maximum value, if the algorithm find a new GOP it will finish with
the first picture of the next GOP (helps minimizing the dts delay)
- fixed a bug where the calculated sending time could be later than
the real DTS time (meaning the decoder wouldn't get the buffer
in time)