lock: turn prepinherit/reacquire into a single context manager Review feedback from Pierre-Yves David. This makes the overall code cleaner and less error-prone, and makes a previously explicitly checked error state impossible.

localrepo: add a note about parentenvvar Review feedback from Pierre-Yves David.

exchange: add "streaming all changes" to bundle2 pulling This is the beginning of client-side support for performing a stream clone using bundle2. The main bundle2 pull function checks whether to perform a streaming clone and outputs a message if so. While we have a duplicate message, it seems easier to have all the bundle2 console writing in one location and in an easy-to-read conditional block.