Add release dates to release notes.
Don't inject manifest if it does not already exist
[test] Fix tests for manifest injection
Fix potential resource leaks
[test] Fix possible race conditions
Remove redundant parameter

Method argument was identical to member variable.
Avoid calling setter in constructor
[test] Add missing copyright notice
[test] Add explicit Plexus config for AbstractInstallerTest

In XMvn Core tests there are two different implementations of
Configurator component.  Explicit Plexus configuration is needed to
choose the right configurator.