MODE-1920:
Expand security context to allow subordinated context.
Security restrictions suppose to be either repository specific or JCR-defined. This may include Access Control support or any additional policy-internal refinements with effects too.
To avoid security collisions the suggestion is to allow construct hierarchy of security contexts where security context provides either repository specific implementation or JCR defined.

In this style session checks permissions in current context and recursively  (if action is not denied) in subordinated contexts.

MODE-1920:
Initial implementation for the Access Control Management as specified by JCR 2.0 spec

MODE-1920:
Commit NullSecurityContext

MODE-1920: Access control management
MODE-1920:  Clean up java-doc. Remove empty methods.
MODE-1920: Add principal implementation to the API
MODE-1920: Fix TCK tests
MODE-1920: Add mode:accessControllable to result set
MODE-1920: Add mode:Acl , mode:Permission, mode:accessControllable to results
MODE-1920: Add methods for execution in access control scope
MODE-1920: Get rid from session instance inside context
MODE-1920: Get rid from session instance inside context
MODE-1920: Add permission checking using ACM within authorizer block
MODE-1920: Clean up code and java-doc
MODE-1920 Corrected compiler warnings and JavaDoc errors