SLING-3068 : do not publish content packages if there was no change, as is the case when a server's set of added modules gets changed (then a PUBLISH_INCREMENTAL with NO_CHANGE gets invoked for already-synched/unchanged modules)

git-svn-id: https://svn.apache.org/repos/asf/sling/branches/tooling-ide-vlt@1524462 13f79535-47bb-0310-9956-ffa450edef68