Fix never expectation deprecation warning logic

[floehopper]

In #681 I added logic to display a deprecation warning about a change I planned to make in #679. However, it turns out the logic in both was faulty as demonstrated in this example where the deprecation warning was incorrectly displayed for the 2nd call to Foo.create_if:

    class Foo
      def self.create_if(condition)
        new if condition
      end
    end

    test "it creates only if condition is true" do
      Foo.expects(:new).never
      Foo.create_if(false)

      Foo.expects(:new).once
      Foo.create_if(true)
    end

This commit adds a new acceptance test to cover an example where the logic was incorrect and updates the logic in Mock#handle_method_call to fix the logic so this new test passes and none of the existing tests fail. Unfortunately the implementation is now rather complicated and hard to follow, but I think it will do for now. I have a couple of ideas for ways to simplify it, but I don't have time to work on that now.

I have updated the equivalent logic in #679 to match the new logic implemented here.

[floehopper]

Released in v2.6.1.