According to the openldap configure script, by disabling
threading support the slurpd daemon would not be built.
- New option: SLURPD to determine whether to build the
replication daemon. (enabled by default). The
replication functionality is not used by every user
so it is desirable to give decision to the user.
- When threading is disabled, reflect the fact that
slurpd is not being built/installed.  This would
also override the user chosen SLURPD option.
- Disable SHELL backend by default.
 Reported by: pointyhat via kris