Bindings with specified `signal` binding behavior (BindingSignaler) are being dirty-checked / not waiting for signals to update the view from view-model getters.

**I'm submitting a bug report**

* **Library Version:**
1.4.0

**Please tell us about your environment:**
* **Operating System:**
Windows 10

* **Node Version:**
8.2.0

* **NPM Version:**
5.3.0

* **JSPM OR Webpack AND Version**
webpack 2.2.1

* **Browsers:**
| Chrome 59 | Firefox 54

* **Language:**
all

**Current behavior:**
When binding in the view to a getter property in the view-model and specifying the `signal:'my-signal'` binding-behavior, the view is streaming the updates instantly.

[_See the gistrun example here_](https://gist.run/?id=da6820af6d16927b42719c4b3f6edeca)

**Expected/desired behavior:**

* **What is the expected behavior?**
The getter property should not be accessed until the BindingSignaler signals an update with the specified string.

* **What is the motivation / use case for changing the behavior?**
Unless I misunderstand, the binding signaler is not behaving as it was intended. Some getters (particularly current-time-based computed properties) should only be accessed every so often, so binding signalers seemed to be the best way to do this, except they are not behaving as I would expect.