Rework lvref.t foreach tests

Rework lvref.t foreach tests

Remove the to-do marker.

Add tests for package vars, too.

Redo the \my &a test.  I’ve decided not to bother with the ‘my &a’
syntax for now (if at all).  It is problematic and needs discussion.
(If ‘my &a’ is allowed in foreach, then it should be allowed else-
where, but ‘my &a;’ would call a stub.)