evolve --rev reordering
-----------------------

  $ cat >> $HGRCPATH <<EOF
  > [defaults]
  > amend=-d "0 0"
  > fold=-d "0 0"
  > [web]
  > push_ssl = false
  > allow_push = *
  > [phases]
  > publish = False
  > [diff]
  > git = 1
  > unified = 0
  > [ui]
  > logtemplate = {rev}:{node|short}@{branch}({phase}) {desc|firstline}\n
  > [extensions]
  > hgext.graphlog=
  > EOF
  $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext/evolve.py" >> $HGRCPATH
  $ mkcommit() {
  >    echo "$1" > "$1"
  >    hg add "$1"
  >    hg ci -m "add $1"
  > }

  $ mkstack() {
  >    # Creates a stack of commit based on $1 with messages from $2, $3 ..
  >    hg update $1 -C
  >    shift
  >    mkcommits $*
  > }

  $ shaof() {
  >   hg log -T {node} -r "first(desc($1))"
  > }

  $ mkcommits() {
  >   for i in $@; do mkcommit $i ; done
  > }

Initial setup
  $ hg init testrevorder
  $ cd testrevorder
  $ mkcommits p _a _b _c
  $ hg phase --public 0
  $ hg up 'desc(_a)'
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo "aaa" > _a
  $ hg amend
  2 new unstable changesets
  $ hg log -G
  @  5:12d519679175@default(draft) add _a
  |
  | o  3:4d156641b718@default(draft) add _c
  | |
  | o  2:4d7242ebb004@default(draft) add _b
  | |
  | x  1:2d73fcd7f07d@default(draft) add _a
  |/
  o  0:f92638be10c7@default(public) add p
  

evolve --rev reorders the rev to solve instability, trivial case 2 revs wrong order
  $ hg evolve --rev 'desc(_c) + desc(_b)'
  move:[2] add _b
  atop:[5] add _a
  move:[3] add _c
  atop:[6] add _b
  working directory is now at 52b8f9b04f83

evolve --rev reorders the rev to solve instability. Harder case, obsolescence
accross three stacks in growing rev numbers.
  $ hg up "desc(_c)"
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ mkcommit d
  $ hg up "desc(_a)"
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ hg amend -m "aprime"
  3 new unstable changesets
  $ hg evolve --rev "desc(_b)"
  move:[6] add _b
  atop:[9] aprime
  working directory is now at 476c9c052aae
  $ hg up "desc(_b) - obsolete()"
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg amend -m "bprime"
  $ hg up "desc(aprime)"
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg amend -m "asecond"
  1 new unstable changesets
  $ hg log -G
  @  12:9a584314f3f3@default(draft) asecond
  |
  | o  11:a59c79776f7c@default(draft) bprime
  | |
  | x  9:81a687b96d4d@default(draft) aprime
  |/
  | o  8:2d86cc7ec3a9@default(draft) add d
  | |
  | o  7:52b8f9b04f83@default(draft) add _c
  | |
  | x  6:59476c3836ef@default(draft) add _b
  | |
  | x  5:12d519679175@default(draft) add _a
  |/
  o  0:f92638be10c7@default(public) add p
  
  $ hg evolve --rev "unstable()"
  move:[11] bprime
  atop:[12] asecond
  move:[7] add _c
  atop:[13] bprime
  move:[8] add d
  atop:[14] add _c
  working directory is now at fd447ba1b20b
  $ hg log -G
  @  15:fd447ba1b20b@default(draft) add d
  |
  o  14:0fc229278e4d@default(draft) add _c
  |
  o  13:c3741b9eafae@default(draft) bprime
  |
  o  12:9a584314f3f3@default(draft) asecond
  |
  o  0:f92638be10c7@default(public) add p