Allow redefinition of f(k)=k in properties, related to #4623

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36902 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fix for #4623

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36903 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e