Updated py-mercurial to 3.8.4.

Update HOMEPAGE and MASTER_SITES.

This is a regularly-scheduled bugfix release.

    bdiff: extend matches across popular lines
    bdiff: remove effectively dead code
    bundle2: don't assume ordering of heads checked after push
    help: document that [subpaths] may rewrite relative paths
    largefiles: fix support for local largefiles while using share extension
    sslutil: synchronize hostname matching logic with CPython

(wiz)