Prior to this change, `__await` would make a deep copy of the continuation stack, but shallow-copy the individual stack frames within it. As a result, continuations appeared to have shallow semantics so long as the continuation stack had only a single frame.
This change also removes an obsolete test from the brief period when we intended continuations to have deep-copy semantics, which has been passing basically by accident.
There's a small update to update_checks.py to handle the recursive directories. Also, I'm only using one level of nesting in this PR but really no reason we can't do more. I'm just not sure what clustering is best right now.
As a pattern, I'm trying to name all failing tests `fail_*.carbon`.
Geoff Romer
Jon Meow