Backport python-ldap unicode fixes to release-1.7.x, add to LDAPBackend.
Review Request #5513 — Created Feb. 20, 2014 and submitted
We had made a fix on master to encode username/password/etc before passing them
into python-ldap for the ADBackend, but never made a similar fix for the
LDAPBackend. This fix also was done on master, rather than release-1.7.x.
