* fix(checkout): classify changes in one place; report missing files (#232)

HasChanges, VisitChanges and Extract's safety check each decided what counts as a change: two SQL WHERE clauses and classifyChange, with an error path whose only job was catching their disagreement. They had already drifted once (HasChanges missed renames until #229).

Now one reader, loadVFileRows, returns every row of a version and one classifier, classifyChange, judges it, in the order fossil's changes command uses: removed > missing > added > renamed > modified. A renamed file that is also edited stays "renamed", so callers that see only the change type do not lose the rename. The WHERE clauses and the malformed-row error are gone.

VisitChanges with a scan now reports a tracked file that is gone from disk as ChangeMissing, which the public API already exposed as "missing" but nothing produced; such files were left out, or shown as added or modified. HasChanges sees a fossil add (rid=0, chnged=0) without a scan, since rid=0 now always means added (#231).

* fix(checkout): treat a non-file at a tracked path as missing (#232)

ScanChanges read each tracked path and failed the whole scan when a directory stood where a file belongs. Fossil's scan reports that path as NOT_A_FILE under its missing filter. The scan now stats first and treats anything that is not a regular file as missing, so Status reports it instead of erroring.

loadVFileRows orders rows by pathname, as fossil's changes lists them. The changelog notes that checkouts written before #231 may hold rid=0 placeholder rows, which HasChanges now counts. check-in: ff9c1af49d user: [email protected] tags: trunk