This support module defines C++ classes which implement drivers for Tektronix
TDS3000 scopes and Rigol DS4000 and DS6000 series scopes.
A virtual base class is implemented to do all IO to the instrument and also
some common functionality.  It defines a handful of virtual functions which
are reimplemented in the instrument specific classes.
Two instrument specific classes are defined, which inherit from the base class.
These derived classes define the instruction set that the instrument supports,
which differ between instruments.
Most of the EPICS record support is in the base class, shared by all instrument
specific classes.  Each instrument specific class add a handfull of commands to
reflect the functionality unique to the instrument supported.

11/3/2015, zms:
added code to drvScope.cpp needed to get traces synchronously.  This means that
the acquisition is tropped, all enabled traces are read in, and the acquisition
is then restarted.  It seems to be working correctly.