Changed the "scope" of LDAP authentication from SCOPE_ONELEVEL to SCOPE_SUBTREE

This allowed our company LDAP server to successfully authenticate against it.  My understanding is that this change should increase the schema's that RB authentication works with.

However, I am by no means an LDAP expert, I just know this is what it took to get it working on our server, and what our IT dept recommended.

Also, this URL of LDAP scope may be instructive: http://www.idevelopment.info/data/LDAP/LDAP_Resources/SEARCH_Setting_the_SCOPE_Parameter.shtml

Works on our company LDAP server.  Of course, I could not test it in other environments, so this change should be considered very carefully.