Widen the result of rangeRem to account for wrap-arounds.
Merge pull request #93 from pjonsson/fix-rangerem

Widen the result of rangeRem to account for signed wrap-arounds.
Improve the test suite to consistently provoke bug #81

The range propagation tests were rather poor in provoking
bugs. The bug in rem, documented in #81 went unnoticed for
several years. This commit fiddles with the generators to
have a distribution which is more likely to provoke bugs.