Fix missing support for the symfony-bundle package type.

Using Composer\Installer\LibraryInstaller to handle the installation of
packages that specify the "symfony-bundle" type is just a temporary solution
while waiting to better define how packages shipping Symfony bundles should
be treated.

bin/composer

@@ -27,6 +27,7 @@ $dm->setDownloader('zip',  new Downloader\ZipDownloader());
 // initialize installation manager
 $im = new Installer\InstallationManager();
 $im->setInstaller('library', new Installer\LibraryInstaller('vendor', $dm, $rm->getLocalRepository()));
+$im->setInstaller('symfony-bundle', new Installer\LibraryInstaller('vendor/bundles', $dm, $rm->getLocalRepository()));
 
 // load package
 $loader  = new Package\Loader\JsonLoader();