util: enable hardlink for some BSD-family filesystems
Since we can now detect filesystems on FreeBSD and OSX. Add their major
filesystems (ufs, zfs for FreeBSD; hfs for OSX) to the hardlink whitelist.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a