annotate: reuse already calculated annotation Before this patch, annotation is re-calculated even if it is already calculated. This may cause unexpected annotation, because already cleared "pcache" ("pcache[f] = []") prevents from scanning ancestors. This patch reuses already calculated annotation if it is available. In fact, "reusable" situation should be seen only on legacy repositories in which a filelog include the merging between the revision and its ancestor, because: - tree is scanned in depth-first without such merging, annotation result should be released soon - recent Mercurial doesn't allow such merging changelog and manifest can include such merging someway, but filelogs can't, because "localrepository._filecommit()" converts such merging request to linear history.