tests/test-revlog.t

hardlink: check directory's st_dev when copying files

Previously, when copying a file, copyfiles will compare src's st_dev with
dirname(dst)'s st_dev, to decide whether to enable hardlink or not.

That could have issues on Linux's overlayfs, where stating directories could
result in different st_dev from st_dev of stating files, even if both the
directories and the files exist in the overlay's upperdir.

This patch fixes it by checking dirname(src) instead. It's more consistent
because we are checking directories for both src and dest.

That fixes test-hardlinks.t running on common Docker setups.

Test for CVE-2016-3630

  $ hg init

  >>> open("a.i", "w").write(
  ... """eJxjYGZgZIAAYQYGxhgom+k/FMx8YKx9ZUaKSOyqo4cnuKb8mbqHV5cBCVTMWb1Cwqkhe4Gsg9AD
  ... Joa3dYtcYYYBAQ8Qr4OqZAYRICPTSr5WKd/42rV36d+8/VmrNpv7NP1jQAXrQE4BqQUARngwVA=="""
  ... .decode("base64").decode("zlib"))

  $ hg debugindex a.i
     rev    offset  length  delta linkrev nodeid       p1           p2
       0         0      19     -1       2 99e0332bd498 000000000000 000000000000
       1        19      12      0       3 6674f57a23d8 99e0332bd498 000000000000
  $ hg debugdata a.i 1 2>&1 | egrep 'Error:.*decoded'
  (mercurial.mpatch.)?mpatchError: patch cannot be decoded (re)