Moved autoload responsibility to e107_class.php

Instead of every independently operating client code figuring out its
own autoload policies, the e107 class file e107_class.php now takes care
of autoloading.

Any client that uses the e107 class will automatically benefit from
autoloading for e107.

This cuts down on potential code duplication, and e107::getSingleton()
is no longer tied to trying to figure out the class path.

This commit REMOVES support for the unused constant flag
E107_DISABLE_AUTOLOAD introduced in
bdef2707b4 and the unused autoload code
introduced in f4cee92890.

thumb.php

@@ -156,7 +156,6 @@ class e_thumbpage
 		@require($tmp.DIRECTORY_SEPARATOR.'core_functions.php');
 		//e107 class
 		@require($tmp.DIRECTORY_SEPARATOR.'e107_class.php');
-		e107::autoload_register(array('e107', 'autoload'));
 
 		$e107_paths = compact(
 			'ADMIN_DIRECTORY',