fixes bug in CompositeFilter.

Problem: ClassCastException in some cases

Solution:
Adding an instance of check at the appropriate place.

Notes:
There may remain an issue with the SUBSTRACTION case.

git-svn-id: file:///svnroot/spoon/trunk/spoon-core@2403 b1f50995-73fd-43b8-8ca2-fbc405a04e82
annotation Facotry #annotation fix to avoid adding to a unmodifiableList
Merge branch 'master' of github.com:INRIA/spoon