[Remops] key size migration

[lists at notatla.org.uk]

> I probably won't move to the larger key size until a new mixmaster package is 
> released for Ubuntu/Debian. I haven't been able to compile the new version on 
> Ubuntu and really don't have time right now to try and fix it.

I haven't compiled it on Ubuntu/Debian but if I do I might make a package.

You haven't posted what snags you found either.  Good bug reports are the
first step toward fixes.