tests/test-hgweb-bundle.t

phabricator: use Phabricator's last node information

This makes it more strict when checking whether or not we should update a
Differential Revision. For example,

  a) Alice updates D1 to content 1.
  b) Bob updates D1 to content 2.
  c) Alice tries to update D1 to content 1.

Previously, `c)` will do nothing because `phabsend` detects the patch is not
changed. A more correct behavior is to override Bob's update here, hence the
patch.

This also makes it possible to return a reaonsable "last node" when there is
no tags but only `Differential Revision` commit messages.

Test Plan:
```
for i in A B C; do echo $i > $i; hg ci -m $i -A $i; done

hg phabsend 0::
# D40: created
# D41: created
# D42: created

echo 3 >> C; hg amend; hg phabsend .
# D42: updated

hg tag --local --hidden -r 2 -f D42
# move tag to the previous version

hg phabsend .
# D42: skipped (previously it would be "updated")

rm -rf .hg; hg init
hg phabread --stack D42 | hg import -
hg phabsend .
# D42: updated
hg tag --local --remove D42
hg commit --amend
hg phabsend .
# D42: updated (no new diff uploaded, previously it will upload a new diff)
```

The old diff object is now returned, which could be useful in the next
patch.

Differential Revision: https://phab.mercurial-scm.org/D121

#require serve

  $ hg init server
  $ cd server
  $ cat >> .hg/hgrc << EOF
  > [extensions]
  > strip=
  > EOF

  $ echo 1 > foo
  $ hg commit -A -m 'first'
  adding foo
  $ echo 2 > bar
  $ hg commit -A -m 'second'
  adding bar

Produce a bundle to use

  $ hg strip -r 1
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/server/.hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg (glob)

Serve from a bundle file

  $ hg serve -R .hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg -d -p $HGPORT --pid-file=hg.pid
  $ cat hg.pid >> $DAEMON_PIDS

Ensure we're serving from the bundle

  $ (get-with-headers.py localhost:$HGPORT 'file/tip/?style=raw')
  200 Script output follows
  
  
  -rw-r--r-- 2 bar
  -rw-r--r-- 2 foo