Update shebang lines of python scripts

/usr/bin/env python is preferable, since it allows us to support
executable scripts on systems where python is installed in places
other than /usr/bin.

Incidentally, this was the only thing I needed to do to confirm
full build support on Windows, so I'm dropping a TODO about Windows
support for the extern generator.

Change-Id: Ice93174428e0d8015d0a7787f07a17e8ac808dc7

build/all.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/build.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #
@@ -283,7 +283,6 @@ class Build(object):
         shakaBuildHelpers.get_source_base(), 'dist',
         'shaka-player.' + name + '.externs.js'))
 
-    # TODO: support Windows builds
     cmd_line = ['node', extern_generator, '--output', output] + files
     if shakaBuildHelpers.execute_get_code(cmd_line) != 0:
       print >> sys.stderr, 'Externs generation failed'

build/check.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/checkversion.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/docs.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/gendeps.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/shakaBuildHelpers.py

@@ -1,5 +1,3 @@
-#!/usr/bin/python
-#
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

build/stats.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #

build/test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.  All Rights Reserved.
 #