These predicates currently take a pair of `IRBlock`s - as it stands, at
most one edge can exist from one `IRBlock` to a given other `IRBlock`.
We may need to revisit that assumption and create an `IREdge` IPA type
at some future date
For ease of reviewing, I've checked in the .expected files from the
AST-based guards library. The next commit accepts output for these tests
and adds tests that use getAST rather than the translation layer.
