graft: abort if --date/user specified with --currentdate/currentuser (BC) They are conflicting options. Let's explicitly ban such combination. Note that this means you need "--no-currentdate --date" to override --currentdate specified in aliases/defaults.

amend: turn currentdate into tri-state bool so config option can be negated Otherwise, rewrite.update-timestap couldn't be overridden by --no-currentdate. FWIW, which do we like? --no-currentdate vs --no-current-date. If the latter is preferred, maybe we can add "graft --current-date" and deprecate "--currentdate".

discovery: improve partial discovery documentation The older documentation could be improved.

discovery: add a simple `addinfo` method The method can directly process a sample result. This makes the main code simpler to follow.

discovery: move missing tracking inside the partialdiscovery object This is the final set that we need to track to have a fully up to date information within the object.

discovery: add a `iscomplete` method to the `partialdiscovery` object The method is used by higher level logic to know if the initial discovery question has been answered.

discovery: update undecided from common directly within partialdiscovery The object knows when there are changes in the "common" set, so it is a good place to update the undecided set.