Add --lock argument to the update command to make this hack explicit and official

doc/03-cli.md

@@ -124,6 +124,8 @@ You can also use wildcards to update a bunch of packages at once:
 * **--optimize-autoloader (-o):** Convert PSR-0 autoloading to classmap to get a faster
   autoloader. This is recommended especially for production, but can take
   a bit of time to run so it is currently not done by default.
+* **--lock:** Only updates the lock file hash to suppress warning about the
+  lock file being out of date
 
 ## require
 

src/Composer/Command/UpdateCommand.php

@@ -35,6 +35,7 @@ class UpdateCommand extends Command
                 new InputOption('dry-run', null, InputOption::VALUE_NONE, 'Outputs the operations but will not execute anything (implicitly enables --verbose).'),
                 new InputOption('dev', null, InputOption::VALUE_NONE, 'Enables installation of require-dev packages (enabled by default, only present for sanity).'),
                 new InputOption('no-dev', null, InputOption::VALUE_NONE, 'Disables installation of require-dev packages.'),
+                new InputOption('lock', null, InputOption::VALUE_NONE, 'Only updates the lock file hash to suppress warning about the lock file being out of date.'),
                 new InputOption('no-custom-installers', null, InputOption::VALUE_NONE, 'Disables all custom installers.'),
                 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.'),
@@ -92,7 +93,7 @@ EOT
             ->setRunScripts(!$input->getOption('no-scripts'))
             ->setOptimizeAutoloader($input->getOption('optimize-autoloader'))
             ->setUpdate(true)
-            ->setUpdateWhitelist($input->getArgument('packages'))
+            ->setUpdateWhitelist($input->getOption('lock') ? array('lock') : $input->getArgument('packages'))
         ;
 
         if ($input->getOption('no-custom-installers')) {