Address additional review of #222, also fixing label types everywhere.

[ioannad]

This addresses additional review comments to PR #222, that were made after it was merged. The last review comment in the discussion suggests to adjust all validation labels to use label types instead of just result types. Should address all occurrences of validation labels.

Additionally adds a boolean catch_label to control frames in the validation algorithm, and some related functionality, fixing the cases for opcodes catch and catch_all.