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.
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None