Cancel pending ajax requests

This extends monaco to allow cancelling of pending ajax requests, if the options.abortPending parameter is set to true.

Simple usage: 

```
var sync = Backbone.sync;
    Backbone.sync = function( method, model, options ) {
        options = options || {};

        if ( options.abortPending === true ) {
            app.requestPool.abortRead(options);
        }
        return  sync.apply(this, arguments);
    };
```