Changes by: Jason Hickey (jyh at cs.caltech.edu)
Date: 2006-06-30 09:56:57 -0700 (Fri, 30 Jun 2006)
Revision: 9414
Log message:

      Added "unsetenv".
      
      Converted some private variables to protected.
      The private.foo is the _right_ thing to do, but
      it does not interact well with 0.9.8 because
      each reference must also be qualified $(private.foo).