Merge pull request #101 from smirolo/v2.5

V2.5 - reference output in text files
Fix RRArbiter test

The output was correct but different.
Fix BindFifthComp test and make it more meaningful
Write test outputs to ./test-outputs

This makes diffing/copying them easier than when they went to /tmp/xxx.
Vastly simplify signed-unsigned operations

We just implement them in terms of signed-signed operations now.
Also, DivUS width inference was incorrect.
Fix Mem test

Use ClassTag instead of either gen() or Manifest
fix len prob in listlookup, use gen in mem instead of direct constructor, and added dot backend
same patch from 2 different paths