verify: keep the revlog open for reading while verifying it This is more explicit. No performances difference were observed.

convert: use `changelogrevision` to fetch changeset data instead of read This `changelogrevision` is a higher level function that will remain simple to use as we refactor the revlog.

revlog: adapt the `reading` check for `unionrepo` We cannot just rely on the length check for the `unionrepo` as the local revlog might be empty while the other revlog contains data. In addition, we need to also open the second revlog for reading when needed.

revlog: adapt the `reading` check for `bundlerepo` We cannot just rely on the length check for the `bundlerepo` as the local revlog might be empty with all data in the bundle.

revlog: make `reading` not crash on empty repository If the revlog is empty, the file might not exist and the open will fails. This is not great, but that details or this is now contained in the revlog itself.

changelog: make the `_delayopener` a real proxy We use the same approach as the `_divertopener`. This make it possible to use other methods of the vfs and not just the `__call__` API.

perf: ensure all readlog's reading is done within a `reading` context We are about to enforce this at the revlog level, so we update the perf code in advance.

perf: change the way we approach revlog reading If the `reading` context manager is available, we should use it over explicit file handle management. This will help us to make file handle management a matter more internal to the revlog.

revlog: document the `rev` method A small docstring does not hurt.

revlog: document the `clearcaches` method A small docstring does not hurt.

revlog: document the `update_caches` method A small docstring does not hurt.

revlog: make the `candelta` method private It is only used internally, so lets make it clear.

revlog: document the `get_streams` method A small docstring does not hurt.

revlog: document the `is_inline_index` method A small docstring does not hurt.

opemvms: add specific files and utilities

openvms: do not check for shebang in openvms script It does not apply to them.

openvms: consider worker costly on OpenVMS As for Windows, the parallel worker feature is less appealing on OpenVMS.

openvms: fix the pager spawning and cleanup Unsurprisingly, pager handling needs some adjustment.

openvms: make process spawning works on OpenVMS We need to adjust some behavior for OpenVMS.

openvms: mark symlink as unsupported on OpenVMS OpenVMS's symlink emulation is broken on some OpenVMS versions, so we better disable them altogether for now.

openvms: duck-punch a bugfix into `environb` object The official Python3 build for OpenVMS has some crippling bug that we need to patch dynamically OpenVMS patches

fastexport: simplify code

branching: merge stable into default

admin-command: add verify command Start using the 'admin' namespace by adding a 'verify' command. Invocation is 'admin::verify'. The idea is to progressively add more focused checks than the existing verify command. To do so we need an advanced way to express what we want to check. The first check for admin::verify is 'working-copy.dirstate' which has no options, because it was an easy first check to implement, which verifies the integrity of the dirstate. This changeset was created with the help of Franck Bret.

transaction: abstract away the detection of an abandoned transaction We're about to add another place where this is used, let's not spill this implementation detail.

commands: add admin namespace In order to stop abusing the 'debug' namespace for non-debug command, it adds a new 'admin' namespace dedicated to 'admin' operations on a repository (i.e commands suitable for administration tasks). This namespace entry would be used to migrate in the future some existing commands from the 'debug' namespace, or other top level commands that may not be directly exposed to end users. (verify command is a perfect candidate for this case)

rust-config: fix incorrect coercion of null values to false As explained in the previous changeset: Probably being too trigger happy about boolean values, I incorrectly set the transform for a `None` to a `Some(false)`. It would cause for example the `ui.formatted` value to be set to `Some(false)`, which turns off the colors among other things, when `None` would trigger the automatic behavior.

rust-config: show default `null` is coerced incorrectly to `false` Probably being too trigger happy about boolean values, I incorrectly set the transform for a `None` to a `Some(false)`. It would cause for example the `ui.formatted` value to be set to `Some(false)`, which turns off the colors among other things, when `None` would trigger the automatic behavior. This is fixed in the next commit.

rust-config: fix fallback to default not parsing the default value When a config item's default is a string, it sometimes needs to be parsed into another type, like in the case of `cmdserver.max-log-size`, that returns a number of bytes from a human-readable amount like `25MB`. The logic for the fix is explained inline.

rust-config: demonstrate a bug when falling back to non-trivial default values The default value (when the user hasn't configured anything) is not run through the value parser, causing a programming error to happen because of type mismatch. This will be fixed in the next commit.