python: Add __future__ imports for python 3 compatibility

Except for src/ext, which we may not want to modify.

Closes ticket 32732.

scripts/codegen/fuzzing_include_am.py

@@ -1,5 +1,10 @@
 #!/usr/bin/python
 
+# Future imports for Python 2.7, mandatory in 3.0
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 FUZZERS = """
 	consensus
 	descriptor

scripts/codegen/gen_server_ciphers.py

@@ -8,6 +8,11 @@
 #
 # Run it on all the files in your openssl include directory.
 
+# Future imports for Python 2.7, mandatory in 3.0
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import re
 import sys
 

scripts/codegen/get_mozilla_ciphers.py

@@ -10,6 +10,11 @@
 # It takes two arguments: the location of a firefox source directory, and the
 # location of an openssl source directory.
 
+# Future imports for Python 2.7, mandatory in 3.0
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import os
 import re
 import sys

scripts/codegen/makedesc.py

@@ -9,6 +9,11 @@
 # I've used this to make inputs for unit tests.  I wouldn't suggest
 # using it for anything else.
 
+# Future imports for Python 2.7, mandatory in 3.0
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
 import base64
 import binascii
 import ctypes