Add resolv_conf_mv=auto option

[pemensik]

It requires stat -c %D to be working. Try to not require stat by checking it is executable first. Should be able to handle both bind-mounted /etc/resolv.conf and atomic move from temp file.

It should work also for issue #19

[rsmarples]

That only works on Linux.

[pemensik]

Is there any portable check to ensure two files are on the same filesystem, but they are not identical file? Something similar to test -ef , but without inode check? I admit I test different Linux flavours, but do not have other VM to test.

Checked openbsd stat manual. Does it need just %d format instead?

[rsmarples]

There is no portable way of working this out. stat format on BSD requires -f, not -c which Linux uses.

[pemensik]

Ah. Okay, maybe configure could sort this detail at build time. It would require just trivial check on build and would not clutter those conditions more than necessary.