OCL interpreter (and other diagnosis utilities) complains from ALE

## Bug description

when using OCL interpreter, for instance for diagnosis or query testing, an error show up in the console:
```
OCL: unstable global EPackage registry for 'http://eclipse.org/emf/ecoretools/ale/diagnostics'.
(See https://bugs.eclipse.org/bugs/show_bug.cgi?id=544165#c14)
Use org.eclipse.ocl.ecore.EcoreEnvironment.checkRegistry() to diagnose the offending contribution.
java.util.ConcurrentModificationException
```

## How to reproduce

Steps to reproduce the behavior:

not easy like many ConcurrentModificationException, but it seems to be more often when the acceleo interpreter is open

## Screenshot