Status of PXS and some IMHO obsolete ops

[Leopold Toetsch]

As stated in the thread "pxs help", the QT example can be expressed in 
terms of NCI. So IMHO the following opsen are obsolete:
- loadext (unused)
- callnative (only in QtHelloWorld.pasm, unimplemented)

And further:
- setline
- setfile
- setpackage
which are already/ought to be in the PBC metadata. Putting "setline"s 
into the PBC stream would also slow down execution.

leo