Review feedback from Pierre-Yves David. A separate line of work is working to
ensure that dirstate writes are written to a separate 'pending' file while a
transaction is active. Lock inheritance currently conflicts with that, so dodge
the issue by simply preventing inheritance while a transaction is running.
Custom merge drivers aren't going to run inside a transaction, so this doesn't
affect that.
We want to prevent locks from being inherited sometimes (e.g. when there's a
currently running transaction, which will break a lot of assumptions we're
making in here.)
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.
This is part of a series that will allow locks to be inherited by subprocesses
in limited circumstances. This patch enables the logic introduced in previous
patches.
The earlier test worked only because the held count went up to 2, so the first
release brought it down to 1. Making a copy of the lock fixes that issue.
