Converted exp and expx to return variable types.

The exp and expx rules in the .y file needed to be updated to return the
variable type rather than just the record type class because it doesn't
support the value necessary to actually generate code for the operations
represented in the source.

 On branch p3_conversion
 Changes to be committed:

	modified:   VarRec.C
	modified:   VarRec.H
	modified:   ice9.y