Implement newlookupvar() to replace dynamic scope

lookupvar() is shifted to oldlookupvar() and newlookupvar() is added. An
intermediary lookupvar() function will query both and if the answer
varies then it will throw a deprecation warning for dynamic scoping. The
intermediary and old lookup functions may be removed at a later date,
thus completing the transition.

A test case has been introduced to detect dynamic scoping and the
deprecation warning. Slight modifications to the spec test scoping
objects were made to bring them more in line with the real world.

All scope tests pass. When oldlookupvar is replaced, the deprecated
dynamic scoping test case will fail and all other scope test cases will
pass.