use a concurrent map to handle file lock

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1550641 13f79535-47bb-0310-9956-ffa450edef68
skip locking true per default

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1550644 13f79535-47bb-0310-9956-ffa450edef68