rebase: remove complex unhiding code This is similar to Martin von Zweigbergk's previous patch [1]. Previous patches are adding more `.unfiltered()` to the rebase code. So I wonder: are we playing whack-a-mole regarding on `unfiltered()` in rebase? Thinking about it, I believe most of the rebase code *should* just use an unfiltered repo. The only exception is before we figuring out a `rebasestate`. This patch makes it so. See added comment in code for why that's more reasonable. This would make the code base cleaner (not mangling the `repo` object), faster (no need to invalidate caches), simpler (less LOC), less error-prone (no need to think about what to unhide, ex. should we unhide wdir p2? how about destinations?), and future proof (other code may change visibility in an unexpected way, ex. directaccess may make the destination only visible when it's in "--dest" revset tree). [1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-March/094277.html Differential Revision: https://phab.mercurial-scm.org/D644

rebase: use unfiltered repo when loading state Before this patch, `rebase --abort` may fail to do the cleanup: $ hg rebase --abort rebase aborted (no revision is removed, only broken state is cleared) The added test case makes sure `--abort` works in this case. Differential Revision: https://phab.mercurial-scm.org/D643

rebase: do not crash rebasing merge with a parent having hidden successor The added test will crash with previous code. Differential Revision: https://phab.mercurial-scm.org/D640

changegroup: fix to allow empty manifest parts The current chunk reading algorithm relied on counting the number of empty chunks and comparing it to the number of chunk lists it expected (1 list of files for cg1 and cg2, and 1 list of files + 1 list of trees for cg3). This implicitly assumed that both the changelog part and the manifestlog part were never empty (since them being empty would cause it to count it as one list being done, and screw up the count). In our treemanifest code, the manifest section could be empty, so we need to handle that case. This patches refactors that code to be more explicit about how it counts the expected parts. Differential Revision: https://phab.mercurial-scm.org/D646