dirstate: enforce the use of `changing_files` context to change tracking Now that everything is using the new context, we can start enforcing its usage.

dirstate: warn if we write to the dirstate without holding the wlock Writing the dirstate without holding the wlock can race with other update and overwrite important change. The comment questionning the current state of things was right, we should the `wlock` should always cover the dirstate. (Yes, this is me, agreeing with myself, half a decade later).

dirstate: avoid transaction backup/restore if we do not hold the lock Doing overwriting the dirstate content without holding the lock is a recipe for disaster.

dirstate: issue a developer warning on implicit write on wlock release Our goal is to get rid of all these to clarify the writing pattern, so it is time to warn about this (and later, forbid it).