make LDAPConnectionPoolTTL more conservative, use r->request_time rather than

end-of-request time, and only update it after a round-trip with the LDAP
server rather than every time we check back into the pool.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1607960 13f79535-47bb-0310-9956-ffa450edef68