tests/test-revert-flags.t

graft-state: save --base in graft's state, fixing bug with graft --continue

Without this change, running graft --continue after grafting a merge commit using --base
(and encountering conflicts) will output "skipping ungraftable merge revision" even though
we specified a base in the initial graft command.

Graft's improve behaviour is reflected in test-graft.t.

Differential Revision: https://phab.mercurial-scm.org/D8578

#require execbit

  $ hg init repo
  $ cd repo
  $ echo foo > foo
  $ chmod 644 foo
  $ hg ci -qAm '644'

  $ chmod 755 foo
  $ hg ci -qAm '755'

reverting to rev 0

  $ hg revert -a -r 0
  reverting foo
  $ hg st
  M foo
  $ hg diff --git
  diff --git a/foo b/foo
  old mode 100755
  new mode 100644

  $ cd ..