bdiff: add version to help detect breaking binary changes Previously, we have no way to detect if a compiled .so file could be used or not, and blindly load it if it exists. Usually we carefully maintain compatibility of .so and fallback to pure code gracefully. But if we stick to the rules, certain nice changes will be impossible to make in a clean way. This patch adds a "version" constant to the module so we can detect inconsistency and take appropriate actions (warn, abort, fallback to pure, run make automatically) in module loader.

obsmarker: add an experimental flag controlling "operation" recording It seems better to introduce the experiment behind a flag for now as there are multiple concerns around the feature: * Storing operation increase the size of obsolescence markers significantly (+10-20%). * It performs poorly when exchanging markers (cannot combine command names, command name might be unknown remotely, etc)

run-tests: remove references to Python 2.6 These are the obvious ones. There is tons of code in this file implementing features from unittest that weren't present in Python 2.6. But that's for other patches.

dirstate: mark {begin,end}parentchange as deprecated (API)

merge: migrate to context manager for changing dirstate parents

localrepo: migrate to context manager for changing dirstate parents

context: migrate to context manager for changing dirstate parents

rebase: migrate to context manager for changing dirstate parents

mq: migrate to context manager for changing dirstate parents

dirstate: introduce new context manager for marking dirstate parent changes