Change: addRule removes previous rule with same name if that exists

[PawelStroinski]

Please see unit test. Unfortunately this is breaking change.

[crissdev]

@PawelStroinski I think if you augment the rule object with a replace option and change addRule and addAnnonymousRule methods, this won't be a breaking change anymore. The starting point for this would be addExtender in this case. This would allow rules like the following to be defined:

var obsv = ko.observable().extend({required: true});
obsv.extend({required: {replace: true, params: false}});

{replace: true} would tell the API to replace the rule. Since I don't see similar functionality documented anywhere this shouldn't be considered a breaking change.

Other thoughts, anyone?