Add failed test: Method calls from calls not assert on tracer

Consider

```ruby
class Post
  def valid?
    nil
  end

  def validate
    valid?
  end
end

real_model = Post.new
mock_model = SimpleMock.new real_model
mock_model.expect :valid?, true
mock_model.validate # => nil
mock_model.verify # => raises MockExpectationError
```

Yes, the *old* method has been called.
Tracer didn't receive `assert` call.

A test for this situation is added by this commit.
Yes, this situation is absent in docs and tests but I thing it's a non-normal.

I think there is key of this problem
(from <http://stackoverflow.com/questions/18163877/strange-simpledelegator-behavior/18164211>):

```ruby
require 'delegate'

class Foo < SimpleDelegator
  def meth
    p 'new_meth'
  end
end

class Bar
  def meth
    p 'old_meth'
  end

  def bar_meth
    meth
  end
end

bar = Bar.new
foo = Foo.new(bar)
foo.meth      #=> "new_meth"
foo.bar_meth  #=> "old_meth"
```

*New* method has been called from *straight*.
But *old* method has been called from *other* call.