Note that this completely disables the newly added keywords 'play' and 'ui' for unversioned code to allow using them as identifiers as I have found at least one mod that uses a variable named 'play' that would have been rendered broken otherwise.
This also disables many ZScript only keywords for other parsing jobs.
- fixed the return type checks in CallStateChain. These made some bogus assumptions about what return prototypes to support and would have skipped any multi-return function whose first argument was actually usable.
