disable prepend option on update

src/Composer/Command/UpdateCommand.php

@@ -44,7 +44,8 @@ class UpdateCommand extends Command
                 new InputOption('no-scripts', null, InputOption::VALUE_NONE, 'Skips the execution of all scripts defined in composer.json file.'),
                 new InputOption('no-progress', null, InputOption::VALUE_NONE, 'Do not output download progress.'),
                 new InputOption('verbose', 'v|vv|vvv', InputOption::VALUE_NONE, 'Shows more details including new commits pulled in when updating packages.'),
-                new InputOption('optimize-autoloader', 'o', InputOption::VALUE_NONE, 'Optimize autoloader during autoloader dump')
+                new InputOption('optimize-autoloader', 'o', InputOption::VALUE_NONE, 'Optimize autoloader during autoloader dump'),
+                new InputOption('no-prepend', null, InputOption::VALUE_NONE, 'Disables the prepending of the autoloader')
             ))
             ->setHelp(<<<EOT
 The <info>update</info> command reads the composer.json file from the
@@ -107,6 +108,7 @@ EOT
             ->setOptimizeAutoloader($input->getOption('optimize-autoloader'))
             ->setUpdate(true)
             ->setUpdateWhitelist($input->getOption('lock') ? array('lock') : $input->getArgument('packages'))
+            ->setPrepend(!$input->getOption('no-prepend'))
         ;
 
         if ($input->getOption('no-plugins')) {