Fixed fall-through/refusal logic.
Added the reject_on_miss option to allow fall-through for unauthenticated users.
Removed error for empty password.
Split try/except to raise appropriate warnings on bind failures.
Added unbind calls in failure conditions.
Added empty password checks back to avoid conversion of the bind requests to anonymous authentication.
Cleanup of the bind_dn behavior and addition of the reject_on_miss option.