IPv6 support with NAPTR/SRV
Send responses on transport failure (fixes #394)
Merge branch 'dev' into ipv6_fixes
UT fixes
Code review mark-ups
Merge pull request #398 from Metaswitch/ipv6_fixes

[Reviewer: Mike] IPv6 fixes
Merge branch 'master' of github.com:Metaswitch/sprout into sto643