Optionally use a "guest user" binding prior to searching real user login in LDAP-based authentication

Review Request #729 — Created Jan. 30, 2009 and submitted — Latest diff uploaded

Review Board SVN (deprecated)
As noted in http://reviews.review-board.org/r/704/ some LDAP servers prohibite anonymous searches so binding is needed to perform other operations. But unlike the 704 this solution still allows to use complex LDAP hierarchy where users' "login" strings can't be expressed as a fixed pattern like 'uid=%s,ou=users,dc=example,dc=com'.