infinitepush: opt out of changegroup3 unless explicitly configured
This is currently a no-op, as changegroup3 is disabled by default. But when it
is enabled, it changes the hash names of the bundle files. As I don't use this
extension, I have no idea if that's OK or not. So keep the current default
behavior until we can get more info from actual users, while allowing them to
opt-in for testing purposes.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).