merge default into stable for 4.9 release

update: fix edge-case with update.atomic-file and read-only files We used to create the tempfile with the original file mode. That means creating a read-only tempfile when the original file is read-only, which crash if we need to write on the tempfile. The file in the working directory ends up being writable with and without the atomic update config, so the behavior is the same.

scmutil: drop unreachable except clause socket.error is a subclass of IOError, which we catch higher up. It seems to have been this way since 020a896a5292 (dispatch: sort exception handlers, 2009-01-12), so let's celebrate the 10 year anniversary (a few days late) of it being wrong by deleting it. Differential Revision: https://phab.mercurial-scm.org/D5626

tests: suppress "Checked out 1 paths of <hash>" from modern git test-convert-git.t is failiing since git commit 0f086e6dca (checkout: print something when checking out paths, 2018-11-13). Suppress the new output by disambiguating the arguments with a "--" separator. Differential Revision: https://phab.mercurial-scm.org/D5625

revlog: document that mmap resources are released implicitly by GC It's okay-ish, but currently the open fd and the mapping itself are leaked until the indexdata is deallocated. If revlog had close(), the underlying resources should be closed there as well, but AFAIK there's no such hook point.

ui: proxy protect/restorestdio() calls to update internal flag It should be better to manage the redirection flag solely by the ui class.

ui: move protectedstdio() context manager from procutil This is a follow-up series for 23a00bc90a3c, "chgserver: do not send system() back to client if stdio redirected." The function is renamed using ui terms.

cext: clang-format new code coming from stable branch

match: support rooted globs in hgignore In a .hgignore, "glob:foo" always means "**/foo". This cannot be avoided because there is no syntax like "^" in regexes to say you don't want the implied "**/" (of course one can use regexes, but glob syntax is nice). When you have a long list of fairly specific globs like path/to/some/thing, this has two consequences: 1. unintended files may be ignored (not too common though) 2. matching performance can suffer significantly Here is vanilla hg status timing on a private repository: Using syntax:glob everywhere real 0m2.199s user 0m1.545s sys 0m0.619s When rooting the appropriate globs real 0m1.434s user 0m0.847s sys 0m0.565s (tangentially, none of this shows up in --profile's output. It seems that C code doesn't play well with profiling) The code already supports this but there is no syntax to make use of it, so it seems reasonable to create such syntax. I create a new hgignore syntax "rootglob". Differential Revision: https://phab.mercurial-scm.org/D5493

resolve: fix mark-check when a file was deleted on one side (issue6020) wvfs.open raises an error if one of the files does not exist. Ignoring the error if it's ENOENT is done in several other places in this code, so I'm in good company :) Differential Revision: https://phab.mercurial-scm.org/D5243