value used for checking frame range.

Added missing code to look for the latest available sample of a differential
channel when the beginning frame didn't have a sample.

When resyncing channels, the code advances a byte at a time, versus 4 bytes, which
caused problems when the frame marker was skipped.

same values as the contstructor.  This is to ensure a class instance
can be re-used without destruction/construction (as when used within
the matlab interface).

Added function to provide the information about a single channel.

when including matlab.  There must have been some #defined symbol that
caused the conflict.