Py3 fixes

doc/conf.py

loopy/__init__.py

loopy/auto_test.py

loopy/check.py

loopy/codegen/__init__.py

loopy/codegen/control.py

loopy/codegen/expression.py

loopy/codegen/instruction.py

loopy/codegen/loop.py

loopy/compiled.py

loopy/context_matching.py

loopy/isl_helpers.py

loopy/kernel/__init__.py

loopy/kernel/array.py

loopy/kernel/creation.py

loopy/kernel/tools.py

loopy/padding.py

loopy/precompute.py

loopy/preprocess.py

loopy/schedule.py