context: add workingcommitctx for exact context to be committed Before this patch, "workingctx" is also used for the context to be committed. But "workingctx" works incorrectly in some cases. For example, even when only some of changed files in the working directory are committed, "status()" on "workingctx" object for committing recognizes files not to be committed as changed, too. As the preparation for fixing these issues, this patch chooses adding new class "workingcommitctx" for exact context to be committed, because switching by the flag (like "self._fixedstatus" or so) in some code paths of "workingctx" is less readable and maintenancable.