phabricator: add commenting to phabsend for new/updated Diffs
Especially useful when sending updates to existing Revisions so one can specify
the sort of changes e.g. "Address review comments" or "Rebase to tip"
If the diff content hasn't changed then it only needs a metadata update which
doesn't show in the Phabricator updates UI, so don't add a comment that will.
Differential Revision: https://phab.mercurial-scm.org/D6496
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev linkrev nodeid p1 p2
0 0 b80de5d13875 000000000000 000000000000
1 1 0376abec49b8 000000000000 000000000000
$ cd ..