Allow anonymous access to be disabled.
This adds a new config switch (nsslapd-allow-anonymous-access) that
allows one to restrict all anonymous access. When this is enabled,
the connection displatch code will only allow BIND operations through
for an unauthenticated user. The BIND code will only allow the
operation through if it's not an anonymous or unauthenticated BIND.
I also fixed a missing capability in the SELinux policy that I ran
into while testing this patch.