[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.
I see, very very related: http://stackoverflow.com/questions/4813055/programmatically-determining-max-value-of-a-signed-integer-type