fix(ngMessage): make ngMessage compatible with ngBind

Fixes angular#8089
Closes angular#13074

BREAKING CHANGE:

ngMessage is now compiled with a priority of 1, which means directives
on the same element as ngMessage with a priority lower than 1 will
be applied when ngMessage calls the $transclude function.
Previously, they were applied during the initial compile phase and were
passed the comment element created by the transclusion of ngMessage.
To restore this behavior, custom directives need to have
their priority increased to at least "1".

Author: Narretz

src/ngMessages/messages.js

@@ -572,6 +572,7 @@ angular.module('ngMessages', [])
     * @ngdoc directive
     * @name ngMessageExp
     * @restrict AE
+    * @priority 1
     * @scope
     *
     * @description
@@ -604,6 +605,7 @@ function ngMessageDirectiveFactory() {
     return {
       restrict: 'AE',
       transclude: 'element',
+      priority: 1, // must run before ngBind, otherwise the text is set on the comment
       terminal: true,
       require: '^^ngMessages',
       link: function(scope, element, attrs, ngMessagesCtrl, $transclude) {

test/ngMessages/messagesSpec.js

@@ -372,6 +372,46 @@ describe('ngMessages', function() {
     expect(trim(element.text())).toEqual("Enter something");
   }));
 
+
+  it('should be compatible with ngBind',
+    inject(function($rootScope, $compile) {
+
+    element = $compile('<div ng-messages="col">' +
+                       '        <div ng-message="required" ng-bind="errorMessages.required"></div>' +
+                       '        <div ng-message="extra" ng-bind="errorMessages.extra"></div>' +
+                       '</div>')($rootScope);
+
+    $rootScope.$apply(function() {
+      $rootScope.col = {
+        required: true,
+        extra: true
+      };
+      $rootScope.errorMessages = {
+        required: 'Fill in the text field.',
+        extra: 'Extra error message.'
+      };
+    });
+
+    expect(messageChildren(element).length).toBe(1);
+    expect(trim(element.text())).toEqual('Fill in the text field.');
+
+    $rootScope.$apply(function() {
+      $rootScope.col.required = false;
+      $rootScope.col.extra = true;
+    });
+
+    expect(messageChildren(element).length).toBe(1);
+    expect(trim(element.text())).toEqual('Extra error message.');
+
+    $rootScope.$apply(function() {
+      $rootScope.errorMessages.extra = 'New error message.';
+    });
+
+    expect(messageChildren(element).length).toBe(1);
+    expect(trim(element.text())).toEqual('New error message.');
+  }));
+
+
   // issue #12856
   it('should only detach the message object that is associated with the message node being removed',
     inject(function($rootScope, $compile, $animate) {