[RDY] Remove project-specific integer types: long_u. (2)

This is part of a series of PR's aimed at removing long_u from the codebase.
This PR deals with the following instances of long_u:

- Those within *eval* module.
- Those within *memfile* module.

It continues the work in #656, #757 towards fulfilling #459.
Well, I just changed comment here. Code is as it was before. It's supposed some time in the future a code restyling refactorization would reach this. But I'll change it if you want.