merged branch khepin/better_error_message (PR #4179)

Commits
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43dc19e update exception message so user can know which message has caused the exception

Discussion
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[Translation] Improved error message

Bug fix: [no]
Feature addition: [no]
Backwards compatibility break: [no]
Symfony2 tests pass: [no] -  (no more or less than they were passing before this addition)

Updates an error message in the translator so the developers can know what is the message causing the error.

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by stof at 2012-05-02T12:09:20Z

You should keep it on one line

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by khepin at 2012-05-02T14:05:08Z

done

src/Symfony/Component/Translation/MessageSelector.php

@@ -74,7 +74,7 @@ class MessageSelector
 
         $position = PluralizationRules::get($number, $locale);
         if (!isset($standardRules[$position])) {
-            throw new \InvalidArgumentException('Unable to choose a translation.');
+            throw new \InvalidArgumentException(sprintf('Unable to choose a translation for "%s" with locale "%s".', $message, $locale));
         }
 
         return $standardRules[$position];