hghave: add "py3k" feature to check whether test runs with Python 3.x This patch adds "py3k" feature to check whether test runs with Python 3.x. This check is needed for portability of test code: for example, in the default, modules are imported relatively first with python 2.x, but imported absolutely with Python 3.x.

hghave: add "absimport" feature to check "absolute_import" in __future__ This patch adds "absimport" feature to check whether "absolute_import" exists in __future__, which means supporting module loading by absolute name. This check is needed for portability of test code using "absolute_import", because Python earlier than 2.5 doesn't support it.