tests/test-revert-flags.t

merge: use collections.defaultdict() for mergeresult.commitinfo

We will be storing info from mergeresult.commitinfo to mergestate._stateextras
in upcoming patches, let's make them use same structure so that we don't have to
make much efforts in transferring info from one to other.

Differential Revision: https://phab.mercurial-scm.org/D8921

#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 ..