mod_ldap: Fix unexpected return codes from LDAP lib being coerced

into LDAP_NO_SUCH_ATTRIBUTE + some new tracing.

     trunk patch: http://svn.apache.org/r1687980
                  http://svn.apache.org/r1689694
                  http://svn.apache.org/r1689698
Backports: 1687980, 1689694, 1689698
Submitted by: covener
Reviewied by: covener, wrowe, ylavic



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1690114 13f79535-47bb-0310-9956-ffa450edef68