Merge r1497371 from trunk:

authnzldap: support "none" as a filter to suppress using a search filter,
which is required by some mainframe security products serving native
registry over LDAP.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1605618 13f79535-47bb-0310-9956-ffa450edef68