title: ComboBox fires change event on every keypress
body: <p>I'm trying to build grid with combobox in toolbar, in Grid I will have some informations about employees and combo will allow me to select employee I would like to load those info.</p>
  <p>I've created grid easily, but I have problem with combobox in toolbar: it fires change event every time I type something.</p>
  <pre><code>Ext.define('My.Grid.Combo', {
      extend: 'Ext.form.ComboBox',
      fieldLabel: 'Choose State',
      store: states,
      alias: 'widget.combostates',
      queryMode: 'local',
      displayField: 'name',
      valueField: 'abbr',
      forceSelection: true,
      listeners: {
          change: function (field, newValue, oldValue) {
              console.log(newValue);
          },
          scope: this
      }
  });
  </code></pre>
  <p>Here is my demo: <a href="http://jsfiddle.net/Misiu/LTVXF/" rel="noreferrer">http://jsfiddle.net/Misiu/LTVXF/</a></p>
  <p>Put cursor inside that combo and start typing. After every key press that event is fired (see console)</p>
  <p>I would like to get that event (or other, doesn't matter) to fire after user selects valid element from that checkbox (I'm using forceSelection).<br/>
  I could add <code>editable: false,</code> but I would like to have local filtering after I enter part of valid value.</p>