Only allow self-updates when called from within a phar

src/Composer/Console/Application.php

@@ -66,7 +66,10 @@ class Application extends BaseApplication
         $this->add(new Command\AboutCommand());
         $this->add(new Command\InstallCommand());
         $this->add(new Command\UpdateCommand());
-        $this->add(new Command\SelfUpdateCommand());
         $this->add(new Command\DebugPackagesCommand());
+
+        if ('phar:' === substr(__FILE__, 0, 5)) {
+            $this->add(new Command\SelfUpdateCommand());
+        }
     }
 }