test: generate the `test-sparse-revlog` artifact when slow-test is allowed The `test-sparse-revlog.t` logic requires a large bundle to be generated. This bundle can be reused from one run to the next but its initial generation is slow. With this patch, if the bundle is missing and slow tests are permitted, the bundle will be generated during the test run. This should ensure that CI run this test.

runtest: also update slow test timeout during `#if` clauses For a `#if slow` test to be useful, we need the test timeout to be increased. Without this, the slow section would likely be killed before it finish.

runtest: move slow timeout process earlier in the `_hghave` method Before this changesets, early returns might prevent this logic to apply. It seem safer to run it sooner.

runtest: extract the logic that update timeout for slow tests We want to use the "slow" test logic not only for "#require" clauses but also in "#if" clauses. For this to be useful we need the logic to bump the timeout in at least two spots. The first step it to factor it out.

tests: increase timeout for slow test Test case `test-sparse-revlog.t` need some artifact (a bundle) build before it can run. The artifact is expensive to build, but can be reused from one run to the other. We are about to update that test to make the artifact building automatic if `--allow-slow-tests` is passed. However, we need a bump the timeout a bit to make sure the artifact building as time to finish. We could maybe teach run-tests.py how to directly handle such artifacts. However since there is only one of them for now, this seems premature. There are also some room to speed up the bundle creation for test-sparse-revlog.t

merge with stable

rewriting: add an option for rewrite commands to use the archived phase Using the archived phase for cleanup provide the same effect than stripping, but in a faster, append-only way. We keep the feature experimental for now until it gets a bit more testing.

strip: introduce a soft strip option This is the first user-accessible way to use the archived phase introduced in 4.8. This implements a feature discussed during the Stockholm sprint, using the archived phase for hiding changesets. The archived phase behaves exactly as stripping: changesets are no longer visible, but pulling/unbundling them will make then reappear. The only notable difference is that unlike hard stripping, soft stripping does not affect obsmarkers. The next changeset will make use of the archived phase for history rewriting command. However, having a way to manually trigger the feature first seems a necessary step before exposing users to this phase; there is a way to un-archived changesets (unbundling), so there must be a way to archive them again. Adding a flag to strip is a good way to provide access to the feature without taking a too big risk on the final UI we want. The flag is experimental so it won't be exposed by default. Using the archived phase is faster and less traumatic for the repository than actually stripping changesets.

branchcache: move loading of branch names and nodes into it's own function This will help me in implementing lazy loading of the branchcache in upcoming patches. Differential Revision: https://phab.mercurial-scm.org/D6023

rebase: add missing dashes in help text