Model description: add a -makeFrozen method to make an ETModelElementDescription or any subclass immutable

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/EtoileFoundation@10245 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
remove accidentally committed directory

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/EtoileFoundation@10246 7b3f36aa-e6db-49c1-8b4c-66eac1997e64