The LDAP server at my (very large) company would not authenticate with
reviewboard using LDAP.  The problem was the SCOPE settings used in
ldapo.search_s() in accounts/backends.py

It was set to: SCOPE_ONELEVEL
I changed it to: SCOPE_SUBTREE

This was in 2 places in backends.py (which is all of the instances of
SCOPE_ONELEVEL).

This was the setting used in our company's example script which is why I
tried it.

When I changed both instances is accounts/backends.py it was able to
authenticate properly against our LDSP.

Based on the following, I think this is a better value for this script and
likely to work with more varied LDAP schemes:
http://www.idevelopment.info/data/LDAP/LDAP_Resources/SEARCH_Setting_the_SCOPE_Parameter.shtml