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

tests/python_version/python_version.py

-#!/usr/bin/python
+#!/usr/bin/env python
 # Copyright (c) 2011 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.
 
 import sys
 
 print "CURRENT CONFIG"
 print sys.version
 
 
 pver = sys.version.split()[0]
 print "CURRENT VERSION"
 print pver
 
 if pver < "2.4":
   print "ERROR Python version is too old"
   sys.exit(-1)
 
 # NOTE: we may want to guard against this as well
 #if pver > "2.6":
 #  print "ERROR Python version is too new"
 #  sys.exit(-1)
 
 print "Python version is OK"
 sys.exit(0)