resolv.conf issues

There are several issues related with DNS and the @/etc/resolv.conf@ file. This issue will serve as realtion.

(from redmine: created on 2014-06-03, closed on 2014-07-10, relates #4633 (closed), relates #4823 (closed), relates #5655 (closed), relates #5036 (closed), relates #5691 (closed), relates #5730 (closed))