dirstate-item: add a "second_ambiguous` flag in the mtime tuple This will be used to support the `mtime-second-ambiguous` flag from dirstate v2. See format documentation for details. For now, we only make it possible to store the information, no other logic have been added. Differential Revision: https://phab.mercurial-scm.org/D11842

dirstate: drop comparison primitive on the timestamp class All comparison are now managed without using operator : - the status mtime comparisons is handled by the DirstateItem, - the fixup reliability check, - the update "hack". So we no longer needs the operator and should discourage its usage. Differential Revision: https://phab.mercurial-scm.org/D11841