expanded file read error message, now checks to see if either eof or rerror are set and outputs an error message stating what was set.

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.