sidedatacopies: only read from copies when in this mode If we know we expect data from sidedata, we read them from sidedata and nothing else. This avoid looking into extra for revision without sidedata entries. Such revision will be introduced in the next changesets. Differential Revision: https://phab.mercurial-scm.org/D7067

dirs: remove mutable string optimization at all As far as I can see, the optimization trick has been dead since 42e89b87ca79 "dirs: speed up by storing number of direct children per dir". After 42e89b87ca79, the key variable is cleared to NULL at each iteration.