test return values of aassign with various elements on LHS

test return values of aassign with various elements on LHS

* hash on LHS followed by array, other hash or scalar,
  for example (%h, @a) = (...);

* above with normal RHS, with duplicates, odd elements
  and combination.

* inspect elements returned by aassign for lvaluedness

* assign doesn't return elements that were just cleared