SLING-2989 : using filesystem-absolute sync-path to ensure VltSerializationManager.isSerializationFile works for serializations of node into the format 'node-name.xml'

git-svn-id: https://svn.apache.org/repos/asf/sling/branches/tooling-ide-vlt@1524373 13f79535-47bb-0310-9956-ffa450edef68