[mythtv-cmyth] Handle extended TS streams: M2TS, ATSC 8-VSB, ISDB-T, DVB-T/C/S

- M2TS packet size is 192 bytes: 4B for timer + MTS packet
- ATSC 8-VSB packet size is 208: MTS packet + 20B for FEC
- ISDB-T packet size is 204: MTS packet + 16B for FEC
- DVB-T/C/S packet size is 204: MTS packet + 16B for FEC

At first sync it checks TS stream and selects packet size after
reaching the best score. Reached score varies from 2
(TS_CHECK_MIN_SCORE) to 10 packets (...MAX_SCORE), depending on
collisions (normal use 624 packets for QOS). Encapsulated TS packet is
not affected ans keep original size of 188 bytes. Once packet size is
discovered, function GoNext() will move to sync byte of next TS packet
and will discard unused data using selected size. Also it allows to
check stream at startup and break it if invalid returning
AVCONTEXT_TS_NOSYNC.
[mythtv-cmyth] Cosmetics in elementaryStream.cpp