It would be really nice if rawGBMatrixLift would always return (into an int* of
mine) whether the remainder turned out to be nonzero.  Then for functions like
"extend" the checking could happen as quickly as possible.

DONE: added return value to rawGBMatrixLift, 20 Oct 2008.

to do: add tests for this function to make sure the zero/non-zero logic is
correct, do this after Dan changes function in the front end.
