Python 3 compat.

Try to keep our Python sources compatible with both Python 2.7 and 3.

Check with 'pylint --py3k' and 'python -3'.

meta/build.py

@@ -2,6 +2,7 @@
 #
 # This script is run from src/libcretonne/build.rs to generate Rust files.
 
+from __future__ import absolute_import
 import argparse
 import isa
 import gen_instr