Fix python scripts in src/build/

build/dir_exists.py

Index: build/dir_exists.py
diff --git a/build/dir_exists.py b/build/dir_exists.py
old mode 100644
new mode 100755
index d1c194f545b7cd16f521af18779f8d86117905ac..0a89bc87bbf6dab98c4d6d6aaf85848c96e4ca3d
--- a/build/dir_exists.py
+++ b/build/dir_exists.py
@@ -1,10 +1,15 @@
 #!/usr/bin/env python
-# Copyright (c) 2009 The Chromium Authors. All rights reserved.
+# Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
+"""Writes True if the argument is a directory."""
 
 import os.path
 import sys
 
-sys.stdout.write(str(os.path.isdir(sys.argv[1])))
-sys.exit(0)
+def main():
+  sys.stdout.write(str(os.path.isdir(sys.argv[1])))
+  return 0
+
+if __name__ == '__main__':
+  sys.exit(main())