Revert changeset c67920d78248.
It breaks 'hg merge && hg up -c REV' when files exist only in one of the
manifests, making hg throw a traceback like:
abort: impossible time zone offset: 4444444
transaction abort!
rollback completed
abort: invalid date: '1\t15.1' see hg(1) manual page for details
transaction abort!
rollback completed
abort: invalid date: 'foo bar' see hg(1) manual page for details
transaction abort!
rollback completed
abort: invalid date: ' 1 4444' see hg(1) manual page for details
transaction abort!
rollback completed
abort: date exceeds 32 bits: 111111111111
transaction abort!
rollback completed
trouble committing bar!
abort: No such file or directory: .../test/bar