STYLE: avoid deprecation warnings for autoPtr set() method

- set() was silently deprecated in favour of reset() FEB-2018
  since the original additional check for overwriting an existing
  pointer was never used. The reset(...) name is more consistent
  with unique_ptr, tmp etc.

  Now emit deprecations for set().

- use direct test for autoPtr, tmp instead of valid() method.
  More consistent with unique_ptr etc.

STYLE: eliminate redundant ptr() use on cloned quantities