Do not set $dirty flag on init

Author: dmitry-dedukhin

src/select2.js

@@ -120,6 +120,9 @@ angular.module('ui.select2', []).value('uiSelect2Config', {}).directive('uiSelec
                 elm.select2('val', controller.$viewValue);
                 // Refresh angular to remove the superfluous option
                 elm.trigger('change');
+                if(newVal && !oldVal) {
+                  controller.$setPristine(true);
+                }
               });
             });
           }