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

pnacl/driver/pnacl-opt.py

-#!/usr/bin/python
+#!/usr/bin/env python
 # Copyright (c) 2012 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.
 #
 # IMPORTANT NOTE: If you make local mods to this file, you must run:
 #   %  pnacl/build.sh driver
 # in order for them to take effect in the scons build.  This command
 # updates the copy in the toolchain/ tree.
 #
 
@@ skipping 34 matching lines @@
 def get_help(unused_argv):
   # Set errexit=False -- Do not exit early to allow testing.
   # For some reason most the llvm tools return non-zero with --help,
   # while all of the gnu tools return 0 with --help.
   # On windows, the exit code is also inconsistent =(
   code, stdout, stderr = driver_tools.Run('${LLVM_OPT} -help',
                                           redirect_stdout=subprocess.PIPE,
                                           redirect_stderr=subprocess.STDOUT,
                                           errexit=False)
   return stdout