tests/test-issue612.t

revset: add optimization for heads(commonancestors())

Previously, the only way to get these commits were (tested on
mozilla-central):

hg perfrevset 'heads(::a7cf55 and ::d8b15)'
! wall 4.988366 comb 4.960000 user 4.780000 sys 0.180000 (best of 3)

After this patch:

(python)
hg perfrevset 'heads(commonancestors(a7cf55 + d8b15))'
! wall 0.002155 comb 0.000000 user 0.000000 sys 0.000000 (best of 1107)

(C)
hg perfrevset 'heads(commonancestors(a7cf55 + d8b15))'
! wall 0.000568 comb 0.000000 user 0.000000 sys 0.000000 (best of 4646)

https://bz.mercurial-scm.org/612

  $ hg init
  $ mkdir src
  $ echo a > src/a.c
  $ hg ci -Ama
  adding src/a.c

  $ hg mv src source
  moving src/a.c to source/a.c

  $ hg ci -Ammove

  $ hg co -C 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo new > src/a.c
  $ echo compiled > src/a.o
  $ hg ci -mupdate
  created new head

  $ hg status
  ? src/a.o

  $ hg merge
  merging src/a.c and source/a.c to source/a.c
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg status
  M source/a.c
  R src/a.c
  ? src/a.o