Remove the uvshrink logic and keep the unveil list in the order of insertion.

Remove the uvshrink logic and keep the unveil list in the order of insertion.
unveil_lookup() is now doing a dumb linear search. The problem with the
uvshrink logic was that ps_uvpcwd was a pointer into this array and after
compation it pointed to the wrong element. Also future unveil caches would
suffer from the same issue.
OK semarie@