With an input condition of op1 > op2, and evaluating the unsigned 
expression:
     LHS = op1 - op2
range-ops was returning LHS < op1 , which is incorrect as op2 could be 
zero.  This patch adjusts it to return LHS <= op1.

Bootstrapped on x86_64-pc-linux-gnu with no regressions.  Pushed.

Andrew