'System' access to LDAPI without a bind in Samba4

[tridge at samba.org]

Hi Andrew,

 > I'm pretty sure you just specify a SASL mechanism of EXTERNAL, with no
 > data exchanged (where you would put the password or ticket) either way. 

I guess we also need to add some support for this in the s4
ldap_server code in source4/ldap_server/ldap_bind.c, and then add some
OS specific code for getting the uid/gid of the process connecting to
the socket.

Cheers, Tridge