**/*.py: use /usr/bin/env to find python

src/trusted/service_runtime/export_header.py

-#!/usr/bin/python
+#!/usr/bin/env python
 # Copyright (c) 2008 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Tools for exporting Native Client ABI header files.
 
 This module is used to export Native Client ABI header files -- which
 are in the native_client/src/trusted/service_runtime/include directory
 -- for use with the SDK and newlib to compile NaCl applications.
 """
@@ skipping 86 matching lines @@
     return 1
   # endif
   ProcessDir(argv[1], argv[2],
              reduce(os.path.join, UNMODIFIED_DIR, argv[2]))
   return 0
 # enddef
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))
 # endif