Updated the fast decoder to take into account the end of DDL

Updated the fast decoder to take into account the end of DDL
(0xD000000D) trailer words which are generated by our readout electronics.
The decoder auto-detects this trailer and does not
complain if it is missing (unless it is corrupt). This can be turned off by
setting the fAutoDetectTrailer to false. Then one can tell the decoder if it
should expect the trailer or not with the fCheckForTrailer flag.
fCheckForTrailer = true for the read data (or new AliRoot) and
fCheckForTrailer = false for old simulated data.
(Artur)