Add exclude-from-classmap support in validation

src/Composer/Package/Loader/ValidatingArrayLoader.php

@@ -200,7 +200,7 @@ class ValidatingArrayLoader implements LoaderInterface
         }
 
         if ($this->validateArray('autoload') && !empty($this->config['autoload'])) {
-            $types = array('psr-0', 'psr-4', 'classmap', 'files');
+            $types = array('psr-0', 'psr-4', 'classmap', 'files', 'exclude-from-classmap');
             foreach ($this->config['autoload'] as $type => $typeConfig) {
                 if (!in_array($type, $types)) {
                     $this->errors[] = 'autoload : invalid value ('.$type.'), must be one of '.implode(', ', $types);