checkout: fchown symlink to proper uid/gid

When commiting a symlink we do store the uid/gid of the actual
symlink (i.e. not target). However, this was not restored
on non-user-mode checkout as it should.

This commit fixes that, and additionally it ensures xattrs
on symlinks are not set in user-mode checkout.

https://bugzilla.gnome.org/show_bug.cgi?id=741125