“a plaintiff seeking a declaration that restrictive covenants do not affect his property is expected to pay his own costs. He is also expected to pay the costs of any defendants who enter an appearance down to the point in proceedings at which they have had a full opportunity of considering the matter and deciding whether or not to oppose the application. Any defendant who then decides to continue, and appears unsuccessfully before the judge, does so at his own risk as to his own costs at that stage. Such defendant should not however be ordered to pay the plaintiff’s costs.”