System users (SYS_*) now have proper user numbers.

System users (SYS_*) now have proper user numbers.
CtdlFillPrivateContext has been replaced by CtdlFillSystemContext.
CtdlFillSystemContext will create the system user if needed, upgrade the
system user from a user 0 if needed and also load the system user if
needed.
The auto purger now makes a log entry if it encounters a user 0 (not an
Aide message).
The Auto purger will post an Aide message if it encounters a user with
no name and a valid user number. This should NEVER happen.

Test thoroughly before release and needs to be tested thoroughly with
host auth systems too.