`locals()` and `globals()` messes with scope checking

[LightAndLight]

There are three mutable, globally accessible dicts called locals() and globals(), and vars(). When these dicts are modified, new variables are brought into scope. Warn about these usages. Warnings should only occur when it's the built-in definitions that are accessed. If a variable called globals is introduced, shadowing the original, then there's no issue.