Tree.js missing onError for dojo.data fetch method

[Douglas Hays]

dijit/Tree.js:getItemChildren() calls store.fetch but doesn't have a onError handler such as:

function onError(error, request) {
        console.log(error);
}
store.fetch({ query: this.query, onComplete: onComplete, onError: onError});

This is being opened in response to customer feedback.

[bill]

Yup. Dup of #4860.