Log Message:
py-mercurial: update to 4.8.1.

Mercurial 4.8.1 (2018-12-04)

A regularly scheduled bugfix release. Some security fixes are
included, but all are expected to be low-risk.

1.1. commands

    commandserver: get around ETIMEDOUT raised by selectors2

    graft: do not try to skip rev derived from ancestor more than once (issue6024)
    verify: provide unit to ui.makeprogress()

1.2. core

    revlog: fix out-of-bounds access by negative parents read from revlog (SEC)

1.3. extensions

    rebase: abort in-mem rebase if there's a dirty merge state
    rebase: fix dir/file conflict detection when using in-mem merge

    rebase: fix path auditing to audit path relative to repo root (issue5818)
    rebase: preserve working copy when redoing in-mem rebase on disk

1.4. unsorted

    tests: stabilize test-inherit-mode.t on FreeBSD and macOS (issue6026)