cmdstate: introduce a "saver" contextmanager and use it in place of save()
Previously, the state was only saved in some paths out of these functions. This
can be problematic, if the user ctrl-c's (or `kill -9`'s) the process, or we
exit out of `relocate` for anything besides the "expected" reason, we won't
record that we were in the middle of an evolve.
One of our users has discovered that this leaves hg in a weird state; the user
did something like this:
```
$ hg evolve
<something goes wrong with the merge tool, hits ctrl-c>
<deals with the merge conflicts>
$ hg evolve --continue
abort: no interrupted evolve to continue
$ hg evolve
abort: uncommitted changes
# Note: commands.status.verbose=True is set.
$ hg status
M foo
# The repository is in an unfinished *update* state.
# No unresolved merge conflicts
# To continue: hg update
```
The user did an `hg update`, but it didn't actually do anything besides take it
out of the unfinished update state (the files were still dirty in the working
directory).
Set up some configs
$ cat >> $HGRCPATH <<EOF
> [extensions]
> rebase=
> EOF
$ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH
Test listing orphan changesets
$ hg init r2
$ cd r2
$ echo a > a && hg ci -Am a
adding a
$ echo b > b && hg ci -Am b
adding b
$ echo c > c && hg ci -Am c
adding c
$ hg up 0
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ echo a >> a && hg ci --amend -m a
2 new orphan changesets
$ hg evolve --list
d2ae7f538514: b
orphan: cb9a9f314b8b (obsolete parent)
177f92b77385: c
orphan: d2ae7f538514 (orphan parent)
$ cd ..
Test listing phase-divergent changesets
$ hg init r3
$ cd r3
$ echo a > a && hg ci -Am a
adding a
$ echo b > b && hg ci --amend -m ab
$ hg phase --public --rev 0 --hidden
1 new phase-divergent changesets
$ hg evolve --list
88cc282e27fc: ab
phase-divergent: cb9a9f314b8b (immutable precursor)
$ cd ..
Test listing content-divergent changesets
$ hg init r1
$ cd r1
$ echo a > a && hg ci -Am a
adding a
$ hg up 0
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo b > b && hg ci -Am b
adding b
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo c > c && hg ci -Am c
adding c
created new head
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo d > d && hg ci -Am d
adding d
created new head
$ hg rebase -s 1 -d 2
rebasing 1:d2ae7f538514 "b"
$ hg rebase -s 1 -d 3 --hidden --config experimental.allowdivergence=True
rebasing 1:d2ae7f538514 "b"
2 new content-divergent changesets
$ hg evolve --list
c882616e9d84: b
content-divergent: a922b3733e98 (draft) (precursor d2ae7f538514)
a922b3733e98: b
content-divergent: c882616e9d84 (draft) (precursor d2ae7f538514)
$ hg evolve --list --rev c882616e9d84
c882616e9d84: b
content-divergent: a922b3733e98 (draft) (precursor d2ae7f538514)
$ hg phase -p a922b3733e98
$ hg evolve --list
c882616e9d84: b
content-divergent: a922b3733e98 (public) (precursor d2ae7f538514)
$ cd ..