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/isa/riscv/__init__.py

@@ -24,10 +24,10 @@ RV32G / RV64G
     F, and D instruction sets listed above.
 
 """
-
-import defs
-import encodings
-import settings
+from __future__ import absolute_import
+from . import defs
+from . import encodings
+from . import settings
 
 # Re-export the primary target ISA definition.
 isa = defs.isa