memctx: substate needs to be {} instead of None

Setting substate to None was an oversight in 7cfd94ec5d30 and this patch
corrects it by setting substate to an empty dictionary which matches what
subrepo code expects.

--HG--
branch : stable
revset: optimize baseset.__sub__ (issue4313)

dd716807fd23 regressed performance of baseset.__sub__ by introducing
a lazyset. This patch restores that lost performance by eagerly
evaluating baseset.__sub__ if the other set is a baseset.

revsetbenchmark.py results impacted by this change:

revset #6: roots(0::tip)
0) wall 2.923473 comb 2.920000 user 2.920000 sys 0.000000 (best of 4)
1) wall 0.077614 comb 0.080000 user 0.080000 sys 0.000000 (best of 100)

revset #23: roots((0:tip)::)
0) wall 2.875178 comb 2.880000 user 2.880000 sys 0.000000 (best of 4)
1) wall 0.154519 comb 0.150000 user 0.150000 sys 0.000000 (best of 61)

On the author's machine, this slowdown manifested during evaluation of
'roots(%ln::)' in phases.retractboundary after unbundling the Firefox
repository. Using `time hg unbundle firefox.hg` as a benchmark:

Before: 8:00
After:  4:28
Delta: -3:32

For reference, the subset and cs baseset instances impacted by this
change were of lengths 193634 and 193627, respectively.

Explicit test coverage of roots(%ln::), while similar to the existing
roots(0::tip) benchmark, has been added.

--HG--
branch : stable
resolve: report no argument warning using a hint

With this change resolve and revert produce consistent output when run with no
arguments:

$ hg resolve
abort: no files or directories specified
(use --all to remerge all files)

$ hg revert
abort: no files or directories specified
(use --all to revert all files)

--HG--
branch : stable
bundle2: only use callable return as reply handler

When a bundle2 parts generator returns a non callable value, it should not be
used as a reply handler. The changegroup part generator is already having this
case of behavior when there is no changegroup to push. This changeset prevent a
crash for user of the experimentable bundle2 feature.

--HG--
branch : stable
test-status: add test for removed-and-untracked state (BC)

In Mercurial 3.0, "hg status" can list the same file twice if it was removed
but still exists in working directory, i.e. removed by "hg forget":

  $ hg status --rev 0 removed
  R removed
  ? removed

But since 65cdc6bab91e, untracked state, "?", is no longer displayed in this
example.

I think the new behavior is correct since a file should have single state, but
if it is a bug, this patch should be dropped.

--HG--
branch : stable