test .displayName: require it to be defined in the first place (~> better failure message)
refactor: use lodash's _.isXyz(..)
fix .displayName of nested 'partial' asserts; extract formatting as arguments to `fmtArgs` (surrounded by parens)
refactor: extract `fmt` and `fmtArgs` into util.js
put back in deferred tests, removed tests that are now created automatically, added TODO re `referee.throwOnFailure = false`
add forgotten util.js + tests for it, add script run-tests (for those who can't run `buster-test`)