[mythtv-cmyth] Handles extended TS stream: 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 synchro it check TS stream and select packet size after reaching the best score.
Reached score varies from 2 (TS_CHECK_MIN_SCORE) to 10 packets (...MAX_SCORE),
depending of collisions (norme 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