improved message when alias service is not found

When using the YAML config format, it can be confusing that you need to
prefix the aliased service id with an `@` character when passing it as
a string, but that you have to omit it when using the `alias` attribute:

```yaml
foo: '@app\Foo'

foo:
    alias: 'App\Foo'
```

This commit will enhance the generated error message in cases where the
aliased service id is prefixed with the `@` character in the `alias`
option like this:

```yaml
foo:
    alias: '@app\Foo'
```

Author: xabbuh

Command/ContainerDebugCommand.php

@@ -22,6 +22,7 @@
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
 use Symfony\Component\DependencyInjection\ParameterBag\ParameterBag;
 
@@ -144,7 +145,16 @@ protected function execute(InputInterface $input, OutputInterface $output)
         $options['show_hidden'] = $input->getOption('show-hidden');
         $options['raw_text'] = $input->getOption('raw');
         $options['output'] = $io;
-        $helper->describe($io, $object, $options);
+
+        try {
+            $helper->describe($io, $object, $options);
+        } catch (ServiceNotFoundException $e) {
+            if ('' !== $e->getId() && '@' === $e->getId()[0]) {
+                throw new ServiceNotFoundException($e->getId(), $e->getSourceId(), null, array(substr($e->getId(), 1)));
+            }
+
+            throw $e;
+        }
 
         if (!$input->getArgument('name') && !$input->getOption('tag') && !$input->getOption('parameter') && $input->isInteractive()) {
             if ($input->getOption('tags')) {