fix(ngOptions): iterate over the options collection in the same way as ngRepeat

In `ngRepeat` if the object to be iterated over is "array-like" then it only iterates
over the numerical indexes rather than every key on the object. This prevents "helper"
methods from being included in the rendered collection.

This commit changes `ngOptions` to iterate in the same way.

BREAKING CHANGE:

Although it is unlikely that anyone is using it in this way, this change does change the
behaviour of `ngOptions` in the following case:

* you are iterating over an array-like object, using the array form of the `ngOptions` syntax
(`item.label for item in items`) and that object contains non-numeric property keys.

In this case these properties with non-numeric keys will be ignored.

** Here array-like is defined by the result of a call to this internal function:
https://github.com/angular/angular.js/blob/v1.4.0-rc.1/src/Angular.js#L198-L211 **

To get the desired behaviour you need to iterate using the object form of the `ngOptions` syntax
(`value.label` for (key, value) in items)`).

Closes angular#11733

Author: petebacondarwin

src/ng/directive/ngOptions.js

@@ -344,10 +344,6 @@ var ngOptionsDirective = ['$compile', '$parse', function($compile, $parse) {
 
         for (var index = 0; index < optionValuesLength; index++) {
           var key = (optionValues === optionValuesKeys) ? index : optionValuesKeys[index];
-
-          // Ignore "angular" properties that start with $ or $$
-          if (key.charAt && key.charAt(0) === '$') return;
-
           var value = optionValues[key];
           var locals = getLocals(value, key);
           var viewValue = viewValueFn(scope, locals);