Fixes #1550/#1546. Name hashing change to fix the build

Fixes #1550.

Some tests are failing after merging #1546. See https://travis-ci.org/sbt/sbt/builds/33265884

- actions / join
- compiler-project / inc-ant-style

## what this changes

`inc.Relations.empty` now takes a default parameter `IncOptions.nameHashingDefault` instead of `false`. This changes the semantics of `inc.Analysis.empty` to match the default `IncOptions`.

/review @gkossakowski