Use print_function import everywhere using print.

As requested in
<https://sourceforge.net/p/roundup/mailman/message/36374864/>, to
avoid accidental future addition of print statements incompatible with
Python 3.

Author: jsm28

scripts/contributors.py

@@ -7,6 +7,7 @@
 
 """
 
+from __future__ import print_function
 from subprocess import check_output
 
 # --- output settings

scripts/schema-dump.py

@@ -16,6 +16,7 @@
     "anatoly techtonik <[email protected]>"
 ]
 
+from __future__ import print_function
 import os
 import sys
 from roundup.anypy import xmlrpc_