amend: don't remove unselected removals from memctx When there are removed files in the working copy and they are not selected to be amended into the parent, the `filectxfn` we create for the `memctx` would still return `None` before this patch. That's clearly incorrect; we should return the `filectx` from the unamended commit. Somehow it seems to not matter much except for the case with copies stored in changesets. Thanks to Kyle Lippincott for doing all the debugging and identifying the fix for this issue. Differential Revision: https://phab.mercurial-scm.org/D12573

tests: demonstrate crash on partial amend with copies in changesets See the fix in the next patch for explanation. Differential Revision: https://phab.mercurial-scm.org/D12572

rebase: while rewriting desc hashes, ignore ambiguous prefix "hashes" If a repo is sufficiently large, a six digit number "hash prefix" can somewhat easily reference an ambiguous hash prefix. Differential Revision: https://phab.mercurial-scm.org/D12552

tests: add test demonstrating issue with ambiguous has prefixes during rebase Differential Revision: https://phab.mercurial-scm.org/D12551

help: set the large-file-limit to 10MB This is a minor increase (5%) and makes the doc much clearer. Differential Revision: https://phab.mercurial-scm.org/D12484

help: clarify the unit of `ui.large-file-limit` config Its might be a bit confusing, especially since `large-file.min-size` uses MB. Differential Revision: https://phab.mercurial-scm.org/D12483

debuglock: ignore ENOENT error when unlocking This is consistent with the main `lock.release` code. Differential Revision: https://phab.mercurial-scm.org/D12481