Refuse to start if /etc/resolv.conf cannot be read/parsed

Tor exit nodes currently assume a local nameserver listening on 127.0.0.1 if /etc/resolv.conf cannot be found (or parsed, I would assume). However, in order to mitigate DNS issues with exit nodes (i.e. those described in task #362 (moved)), I think tor should refuse to start (or at least log a warning/error to stderr) if this is the case. Of course, this does not solve all DNS issues, as invalid DNS servers could still easily exist in /etc/resolv.conf, but it will at least act as a basic "dummy proofing" for those chrooting/jailing their tor exit nodes.

[Automatically added by flyspray2trac: Operating System: All]

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