- nx.tcl: * made "/cls/ class ..." using ensemble methods and therefore extensible. * This introduces some definition order dependencies in nx.tcl and some redundancy ("class filter" and "class mixin"), but maybe this can be eliminated.
- nx.tcl: * added parameter option incremental for "property" and "variable" * removed the nonpos argument "-incremental" from "property" and "variable" * adapted regression test for these cases