nx-test.tcl

nx-test.tcl (nx::test case): As (ensemble) methods are currently not covered by the auto-cleanup feature of "nx::test case", I took care of not cleaning up the per-class ensemble slots while the alias is still available. This led to dangling aliases in cases such as:
package req nx::test
nx::Class create ::A
nx::test case tmp {
::A public method "oo ps" {} {;}; # creates ::A::slot::__oo plus alias pointing to it.
}
A create a
a oo ps; # "target "::A::slot::__oo" of alias oo apparently disappeared"

Along the way, modernized nx::test case a little (apply).