upgrade: more standard creation of the temporary repository By using the standard path to create a repository we fill some hole in the current initialization process. The one who triggered this changeset was the lack of extensions initialization.

upgrade: use the repository 'ui' as the base for the new repository The `repo.baseui` contains all the configuration but the one specific to the repository (so it can be used when dealing with local peer and sub- repository). However, we need the repository config to be taken into account when doing the upgrade. Otherwise, the upgrade related config that exists in the repository config won't be taken into account when performing the update. A buggy and surprising behavior. We had to work around protection set around `repo.ui.copy` since we are an uncommon case.

upgrade: add a test to show the repository config being ignored The upgrade process ignores the config within the repository. The next changeset fixes it, but we introduce this test before to show it actually tests our target.

upgrade: register compression as a format variants Compression is a promising vector for speedup, let us make it easier to check the compression used and upgrade existing repository.

debugformat: handle non-boolean value for variant

debugformat: update label depending on value difference The new label highlight areas where the repo format differs from current config or default. This should help people spot area where a repository mismatch with the expected state.

debugformat: add data about the config when verbose In verbose mode, the command also displays the current configuration choice for the variant and the global Mercurial default for it.

debugformat: add a 'debugformat' command The command displays basic data about all format variants registered for repo upgrades. This gives a quick way to peek into a repository format. The 'fm.write()' calls are very independent because more data will be added in later changeset. Having more separate call make the later patch clearer.

upgrade: rename 'removecldeltachain' to 'plain-cl-delta' The new naming is more descriptive of a "state" while the older one was more about "action". I'm looking into command exposing more of data about the state of the repository so "state" oriented work better there. The key has not been made public anywhere outside the debug area so it is fine to update it.

tests: glob away ' that doesn't occur on all platforms in lfs test Differential Revision: https://phab.mercurial-scm.org/D1623