Now we name all the private contexts.

Now we name all the private contexts.
Auto purger will complain if a user 0 has no name or does not have a
SYS_* type name as this is considered a bug.
upgrade module will try to fix up names of user 0 and will delete any
user 0 that does not fit the criteria without warning.
User name Citadel is no longer reserved but all usernames starting SYS_*
are.