Log Message:
py-mercurial: update to 5.5.2.

Make py-expat a full dependency, it is used (indirectly) by an
installed file.

Update rust cargo files list; however, two still don't fetch so keep
rust option disabled.

Mercurial 5.5.2 (2020-10-2)

Regularly scheduled bug fix release.

1.1. commands

    log: fix crash and bad filematcher lookup by -fr'wdir()' PATH

1.2. unsorted

    hgdemandimport: bypass demandimport for _ast module (issue6407)
    hgdemandimport: exclude more sqlalchemy modules

    strip: with --keep, consider all revs "removed" from the wcp \ 
(issue6270)