py3: listify filter() to call len() on it Differential Revision: https://phab.mercurial-scm.org/D5354

rebase: fix dir/file conflict detection when using in-mem merge Differential Revision: https://phab.mercurial-scm.org/D5360

tests: show that in-mem rebase does not find path dir/file conflicts Differential Revision: https://phab.mercurial-scm.org/D5359

extdiff: register the configuration generated commands with a help category Otherwise, 'extdiff' shows up under file management and the rest of the commands are at the bottom under 'Uncategorized'.

loggingutil: document openlogfile() This function will be used later for command-server logging.

loggingutil: extract openlogfile() and proxylogger to new module This module isn't placed under the "utils" package since it needs "ui" to process things. It's called "loggingutil", not "logutil" because the word "log" is too obscure in our codebase.

blackbox: pass in options to _openlogfile() as arguments This prepares for extracting utility function from the blackbox module.

blackbox: just try writing to repo.vfs and update lastlogger on success This is simpler and more robust. Before, an empty ".hg" directory would be created if it's removed after checking vfs.isdir('.').

vfs: add option to not create parent directories implicitly In blackbox, we don't want to create a ".hg" directory by mistake. This provides a race-safe option to achieve that.

repo: add a `wcachevfs` to access the `.hg/wcache/` directory This wvfs will allow us to migrate various cache to the new `wcache` directory. Helping with cache issues with "share".