feat: implement MS Active Directory LDAP_SERVER_FAST_BIND_OID control

[cpuschma]

Requested in #514, this implements the LDAP_SERVER_FAST_BIND_OID, which is described here: https://msdn.microsoft.com/en-us/library/58bbd5c4-b5c4-41e2-b12c-cdaad1223d6a. The implementation is straightforward, as only the control type needs to be sent.

Tests can't be extended for this control, as it's Active Directory specific.

[cpuschma]

Please don't merge this yet, I've got a few additional things to check as I stumbled upon a few forum entries regarding this OID. I'll keep you posted.

[cpuschma]

Available through the recently added extended operations. See:

ldap/extended_test.go

Lines 28 to 41 in 601814b

	func TestExtendedRequest_FastBind(t *testing.T) {
	conn, err := DialURL(ldapServer)
	if err != nil {
	t.Error(err)
	}
	defer conn.Close()
	request := NewExtendedRequest("1.3.6.1.4.1.4203.1.11.3", nil)
	_, err = conn.Extended(request)
	if err != nil {
	t.Errorf("%s failed: %v", t.Name(), err)
	return
	}
	}