tests/test-revlog-packentry.t

tests: stabilize test-persistent-nodemap.t on Windows

Several issues here:

  - Hooks can't invoke shell scripts on Windows, so use `sh` to launch
  - `dd` in MSYS only recognizes `status=noxfer`
  - The `PATH` updating triggered a massive slowdown, but is no longer needed

I have no idea why, but removing the `PATH` update substantially increased the
speed of the test.  It was running finishing at ~4:30 with `--debug` and ~14:50
without it, but now completes in ~2:20 on my Windows laptop.

Differential Revision: https://phab.mercurial-scm.org/D10636

  $ hg init repo
  $ cd repo

  $ touch foo
  $ hg ci -Am 'add foo'
  adding foo

  $ hg up -C null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

this should be stored as a delta against rev 0

  $ echo foo bar baz > foo
  $ hg ci -Am 'add foo again'
  adding foo
  created new head

  $ hg debugindex foo
     rev linkrev nodeid       p1           p2
       0       0 b80de5d13875 000000000000 000000000000
       1       1 0376abec49b8 000000000000 000000000000

  $ cd ..