Unique exception for invalid autoload paths, better handling

Background jobs are tolerant of stale entries left by disabled apps,
which will cause an autoload exception.

lib/autoloader.php

@@ -27,6 +27,8 @@
 
 namespace OC;
 
+use \OCP\AutoloadNotAllowedException;
+
 class Autoloader {
 	private $useGlobalClassPath = true;
 
@@ -129,7 +131,7 @@ class Autoloader {
 				return true;
 			}
 		}
-		throw new \Exception('Path not allowed: '. $fullPath);
+		throw new AutoloadNotAllowedException($fullPath);
 	}
 
 	/**