[Translator] mention that the message id may also be an object that c…

…an be cast to string in TranslatorInterface and fix the IdentityTranslator that did not respect this

IdentityTranslator.php

@@ -59,7 +59,7 @@ public function getLocale()
      */
     public function trans($id, array $parameters = array(), $domain = 'messages', $locale = null)
     {
-        return strtr($id, $parameters);
+        return strtr((string) $id, $parameters);
     }
 
     /**
@@ -69,6 +69,6 @@ public function trans($id, array $parameters = array(), $domain = 'messages', $l
      */
     public function transChoice($id, $number, array $parameters = array(), $domain = 'messages', $locale = null)
     {
-        return strtr($this->selector->choose($id, (int) $number, $locale), $parameters);
+        return strtr($this->selector->choose((string) $id, (int) $number, $locale), $parameters);
     }
 }

TranslatorInterface.php

@@ -23,7 +23,7 @@ interface TranslatorInterface
     /**
      * Translates the given message.
      *
-     * @param string $id         The message id
+     * @param string $id         The message id (may also be an object that can be cast to string)
      * @param array  $parameters An array of parameters for the message
      * @param string $domain     The domain for the message
      * @param string $locale     The locale
@@ -37,7 +37,7 @@ public function trans($id, array $parameters = array(), $domain = null, $locale
     /**
      * Translates the given choice message by choosing a translation according to a number.
      *
-     * @param string  $id         The message id
+     * @param string  $id         The message id (may also be an object that can be cast to string)
      * @param integer $number     The number to use to find the indice of the message
      * @param array   $parameters An array of parameters for the message
      * @param string  $domain     The domain for the message