This file documents the flow of control through the new LDAP logic:


                   UserSearch
                       |
                       |
                 SourceBlock *s;
               search in s->userDb
                    /      \
               ----/        \-----------
              /                         \
          not found                   found
           |                          /   \
           |                         /     \
           |                      LDAP     user list
           |                      user       user
           |                      /  \        |
           |                     /    \-------+
           |                timeout           |
           |                   /              |
      search LDAP ------------/               |
        URL list                              |
          / \                                 |
         /   \                                |
       not   found                            |
     found    |                               |
        |     |                           return success
        \    /
       save both
     states in the
      userDb cache
    i.e. add to userDb
       if necessary
           |
           |
       return found state as success or failure