[krbdev.mit.edu #6347] kadmin -keepold documented as not supported for LDAP but appears to work

[Russ Allbery <rra@stanford.edu> via RT]

This is Debian bug http://bugs.debian.org/480517

The kadmin man page says that -keepold is not supported for the LDAP
database, but it appears to work.  Is the documentation out of date
compared to the implementation, or is this really dangerous and
shouldn't be done?  (If the latter, it probably should be disallowed
somewhere in the code.)