Use correct shebang for python scripts

tools/amalgamate.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 # coding: UTF-8
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this 

tools/c2rst.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this 
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.

tools/generate_statuscode_descriptions.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this 
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.