Forwarding ChangePassword from asp.net provider to IMembershipService. Also fixing an error handling issue in forms auth service.

--HG--
extra : convert_revision : svn%3A5ff7c347-ad56-4c35-b696-ccb81de16e03/trunk%4040941

src/Orchard/Security/Providers/FormsAuthenticationService.cs

@@ -65,6 +65,7 @@ namespace Orchard.Security.Providers {
             int userId;
             if (!int.TryParse(userData, out userId)) {
                 Logger.Fatal("User id not a parsable integer");
+                return null;
             }
             return _modelManager.Get(userId).As<IUser>();
         }

src/Orchard/Security/Providers/OrchardMembershipProvider.cs

@@ -51,7 +51,11 @@ namespace Orchard.Security.Providers {
         }
 
         public override bool ChangePassword(string username, string oldPassword, string newPassword) {
-            throw new NotImplementedException();
+            var service = GetService();
+            var user = service.ValidateUser(username, oldPassword);
+            if (user == null)
+                return false;
+            service.SetPassword(user, newPassword);
         }
 
         public override string ResetPassword(string username, string answer) {