commands: document the layering violation in `manifest --all` This commit fixes the last test failures when using the simple store extension! It turns out that `hg manifest --all` locks the repo and scans for revlogs. This feature was added by 71938479eff9 in 2011. I am debating changing the behavior. But that can occur in another commit. As part of debugging this, I realized that test-manifest.t is the only meaningful tester of `hg manifest --all` and that test was improperly disabled when bundlerepos aren't supported. The test is testing manifest behavior, not whether you can `hg pull` from a bundle. So I changed the test to `hg unbundle` instead. FWIW, I wasted a non-trivial amount of time tracking down this failure. I thought the issue involved Git, which is why I refactored the test to be more deterministic. Never in my mind would I have guessed that code in `hg manifest` would scan revlogs. I should have looked there to begin with. Doh. Differential Revision: https://phab.mercurial-scm.org/D3118