filtering: rename filters to their antonyms Now that changelog filtering is in place, it's become evident that naming the filters according to the set of revs _not_ included in the filtered changelog is confusing. This is especially evident in the collaborative branch cache scheme. This changes the names of the filters to reflect the revs that _are_ included: hidden -> visible unserved -> served mutable -> immutable impactable -> base repoview.filteredrevs is renamed to filterrevs, so that callers read a bit more sensibly, e.g.: filterrevs('visible') # filter revs according to what's visible