search for python, python3, and then python3.1.  Require version 3.1.  Use @PYTHON@ in all .in files, and add run_bigtool.in.  This should cover all script wrappers.

git-svn-id: svn://bind10.isc.org/svn/bind10/branches/parkinglot@336 e5f2f494-b856-4b98-b285-d166d9295462