To test this change, I used a MiniMaxwell which allows me to introduce
jitter, delay, and packet re-ordering in the video stream. I ran for
over 12 hours with no effect on the video and no increase in buffer
size. I'm reattaching the final patch here. I've made 2 basic changes
to the buffering strategy:

1) I now check to see if I and done buffering on both the
ES_OUT_SET_PCR and ES_OUT_SET_GROUP_PCR calls. This causes the buffered
amount to be checked more frequently and prevents over buffering which
I have seen in some instances
2) When ignoring the jitter, I do not flush the buffer and rebuffer,
since I am not increasing the buffer size anyway. Instead I just reset
the PCR and continue on.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>