modified test-nexpr to use relative tolerance, fixed issue with 0
modified test-nexpr to use relative tolerance, fixed issue with 0

nxdao2000/nimble,nimble-dev/nimble,NLMichaud/nimble,NLMichaud/nimble,nxdao2000/nimble,nxdao2000/nimble,NLMichaud/nimble,nimble-dev/nimble,nimble-dev/nimble,nimble-dev/nimble,nimble-dev/nimble,nxdao2000/nimble,NLMichaud/nimble