FELIX-4223 document service event tracking, start code cleanup on way to avoiding collisions between config updates and activation/deactivation

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1523551 13f79535-47bb-0310-9956-ffa450edef68
FELIX-4223 access m_activated more usually under a lock

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1523552 13f79535-47bb-0310-9956-ffa450edef68
FELIX-4223 Use read-write lock to prevent activation/deactivation during config update

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1523553 13f79535-47bb-0310-9956-ffa450edef68
FELIX-4223 minor cleanups

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1523554 13f79535-47bb-0310-9956-ffa450edef68