We used to generate a module T with a serialize() and deserialize() fn,
but this was suboptimal for a number of reasons:
- it required moving serialization into core so that uint etc worked
- it was harder to override the serialization behavior locally
(this is now trivial)
Issue #352Closes#1720
The old checker would happily accept things like 'alt x { @some(a) { a } }'.
It now properly descends into patterns, checks exhaustiveness of booleans,
and complains when number/string patterns aren't exhaustive.
