r17499: Open the main database only the minimum times during a provision.

r17499: Open the main database only the minimum times during a provision.

This causes things to operate as just one transaction (locally), and
to make a minimum of TCP connections when connecting to a remote LDAP
server.

Taking advantage of this, create another file to handle loading the
Samba4 specific schema extensions.  Also comment out 'middleName' and
reassign the OID to one in the Samba4 range, as it is 'stolen' from a
netscape range that is used in OpenLDAP and interenet standards for
'ref'.

Andrew Bartlett