Bug 10908: restore non-anonymous auth_by_bind LDAP options

Bug 10908: restore non-anonymous auth_by_bind LDAP options

Recent changes to LDAP broke auth_by_bind in many situations. This bug
resets the behaviour to what it used to be, however also allows the new
behaviour by adding the 'anonymous_bind' parameter to the LDAP config.

Testing:
    1) Find an LDAP configuration that was broken recently that uses
       auth_by_bind
    2) Apply this patch
    3) See if it works again.
Additionally, testing the original path in the case of 'anonymous_bind'
being set should probably be done too, but I have no idea about the LDAP
server config for that.

Signed-off-by: Ulrich Kleiber <ulrich.kleiber@bsz-bw.de>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>