uncommit: add config option to keep commit by default
We have a Google-internal extension that keeps track of "review units"
(like Phabricator reviews, or Gerrit's Change-Id). This information is
stored outside of the commit. It is updated with rewrites. Every now
and then we get reports from users who are confused because `hg
uncommit` lost track of their review. Keeping the empty commit by
default would reduce this confusion. It may also cause confusion about
the empty commit. This patch adds a config option that lets us easily
test both behaviors on our users.
Differential Revision: https://phab.mercurial-scm.org/D5970
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present