aliastest.tcl

- Implemented "interp alias" support for classes. In some cases. interp-aliased classes worked already without additional code, but e.g. in "... -superclass C ..." it failed. Without this feature, one could not reuse a class with a different namespace, unless it was explicitely "namespace exported" in the source. The problem was the implementation of "::nx::Attribute", which should not be exported in nx (most people do a "namespace import ::nx::*") because there is no need to do so, but ::xotcl::Attribute should reuse it - without subclassing). .... However, we still seem to have a problem, when the interp-aliased Class is exported and imported to a different namespace.
- removed definition of slots from nx, changed regression tests
examples to to ::attribute instead of -slots