Handle unlinking in-use files on virtual drives

Handle unlinking in-use files on virtual drives

        * path.cc (path_conv::set_nt_native_path): New function.
        * path.h (path_conv::set_nt_native_path): Add prototype.
        * syscall.cc (try_to_bin): Handle moving files to the recycler
        accessed via a local virtual drive (subst).  Fix a problem renaming
        the file to the unique replacement name on Samba.  Align comment.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>