add test about cache
Merge remote-tracking branch 'origin/dev' into erik
Check equility during tree creation
Add constraint between concret et structural
Edit Test to catch exceptions
Merge remote-tracking branch 'origin/dev' into erik
Fix test about level Sensor
Merge remote-tracking branch 'origin/dev' into erik

Conflicts:
	gs-kernel/src/test/java/org/genericsystem/kernel/AdjustMetaTest.java
	gs-kernel/src/test/java/org/genericsystem/kernel/PropertyConstraintTest.java
	gs-kernel/src/test/java/org/genericsystem/kernel/RemovableServiceTest.java
	gs-kernel/src/test/java/org/genericsystem/kernel/WeakEquivTest.java
Problem when 2 holders add on concrete
clean