Ban former experimental airlift modules
Update versions for release and surefire plugin

- Release plugin to 2.3.2 (last version before local checkout regression)
- Surefire plugin to 2.14

Explicitly set goals for release plugin, make sure that the sonatype release
profile is not activated accidentially.
remove unnecessary combine.children attributes where the parent has no element.
add a project url
pmd rulesets are now organized slightly different
update guava to 14.0.1
add note about airlift experimental bans
[maven-release-plugin] prepare release 6
[maven-release-plugin] prepare for next development iteration