Adds utility for determining whether or not a request needs to be manually resolved

This is useful for frameworks such as Ember which automatically wait for async
things to end before continuing.

This allows such functions to be overriden and filtered.

For instance:

```js
Ember.$(document).unbind('ajaxSend').bind('ajaxSend', function(e, jqXHR, props) {
  if (pretender.requiresManualResolution(props.type, props.url)) {
    e.stopImmediatePropagation();
  }
});
```