fix(select): support optgroup + select[multiple] combo

Closes #1553

Author: _pants

src/ng/directive/select.js

@@ -265,7 +265,7 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
         var lastView;
         ctrl.$render = function() {
           var items = new HashMap(ctrl.$viewValue);
-          forEach(selectElement.children(), function(option) {
+          forEach(selectElement.find('option'), function(option) {
             option.selected = isDefined(items.get(option.value));
           });
         };
@@ -282,7 +282,7 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
         selectElement.bind('change', function() {
           scope.$apply(function() {
             var array = [];
-            forEach(selectElement.children(), function(option) {
+            forEach(selectElement.find('option'), function(option) {
               if (option.selected) {
                 array.push(option.value);
               }

test/ng/directive/selectSpec.js

@@ -405,6 +405,27 @@ describe('select', function() {
       expect(element).toEqualSelect(['A'], ['B']);
     });
 
+    it('should work with optgroups', function() {
+      compile('<select ng-model="selection" multiple>' +
+                '<optgroup label="group1">' +
+                  '<option>A</option>' +
+                  '<option>B</option>' +
+                '</optgroup>' +
+              '</select>');
+
+      expect(element).toEqualSelect('A', 'B');
+      expect(scope.selection).toBeUndefined();
+
+      scope.$apply(function() {
+        scope.selection = ['A'];
+      });
+      expect(element).toEqualSelect(['A'], 'B');
+
+      scope.$apply(function() {
+        scope.selection.push('B');
+      });
+      expect(element).toEqualSelect(['A'], ['B']);
+    });
 
     it('should require', function() {
       compile(