Harmonize message for 'User has no profile.' and update translator documentation.

plugins/Mapstraction/map.php

@@ -69,6 +69,7 @@ class MapAction extends OwnerDesignAction
         $this->user = User::staticGet('nickname', $nickname);
 
         if (!$this->user) {
+            // TRANS: Client error displayed when referring to a non-existing user.
             $this->clientError(_m('No such user.'), 404);
             return false;
         }
@@ -76,6 +77,7 @@ class MapAction extends OwnerDesignAction
         $this->profile = $this->user->getProfile();
 
         if (!$this->profile) {
+            // TRANS: Error message displayed when referring to a user without a profile.
             $this->serverError(_m('User has no profile.'));
             return false;
         }