LDAP: Support for Active Directory objectGUID

LDAP: Support for Active Directory objectGUID

Adds optional "ldap uuid encoding = string | ms-guid" parameter to afp.conf,
allowing for usage of the binary objectGUID fields from Active Directory.

If left unspecified, "string" is the default, which passes through the ASCII
UUID returned by most other LDAP stores. If set to ms-guid, the internal UUID
representation is converted to and from the binary format used in the
objectGUID attribute found on objects in Active Directory when interacting
with the server.