dirstate-item: add a "second_ambiguous` flag in the mtime tuple...
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