Fixes #3462: make system item be modifiable by system calls
Merge pull request #164 from fanf/bug_3462/make_system_directive_updatable_by_migration_script

Fixes #3462: make system item be modifiable by system calls
Merge branch 'branches/rudder/2.5'

Conflicts:
	rudder-core/src/main/scala/com/normation/rudder/services/policies/DependencyAndDeletionService.scala
	rudder-core/src/main/scala/com/normation/rudder/services/queries/DynGroupUpdaterService.scala
	rudder-core/src/main/scala/com/normation/rudder/services/servers/NewNodeManager.scala
	rudder-web/src/main/scala/bootstrap/liftweb/checks/CheckMigrationDirectiveInterpolatedVariablesHaveRudderNamespace.scala