fix suspicious use of ldap file descriptors
fix suspicious use of ldap file descriptors

One problem: when openldap library handles reconnect and succeeds, there
is no guarantee that the file descriptor will stay the same - but binding
didn't detect this.

Second problem: calling ev_io_set on c->read_watcher_ that may be active is
explicitly forbidden in libev docs.

jeremycx/node-LDAP,jeremycx/node-LDAP,jeremycx/node-LDAP,jeremycx/node-LDAP