Timely cleanup of SVs that are cloned into a new thread but then discovered
to be orphaned (i.e. their owners are -not- cloned) (e42956)
+Don't accidentally clone lexicals in scope within active stack frames in
+the parent when creating a child thread (RT #73086) (05d04d).
+
Avoid loading feature.pm when 'no 5.13.2;' or similar is encountered (faee19).
Trap invalid use of SvIVX on SVt_REGEXP when assertions are on (e77da3)