This patch allows user to specify that socket binding can fail. On IPv4 there
is a ip_nonlocal_bind sysctl that can be set, however for IPv6 there is not
this call and it is unlikely to be implemented kernel-side.

Fixes PowerDNS/pdns#344
rebase to HEAD
Merge branch 'master' into nonexist-fail-bind
add in -fail conf options
Merge pull request #1129 from mzealey/nonexist-fail-bind

This patch allows user to specify that socket binding can fail. On IPv4 ...