(PUP-636) Ignore generated file
(PUP-638) Add a pick_default() function that always returns a value.

This version of pick() does not error out, instead always returning at least
the last argument, even if that too has no "real" value.
Merge branch 'DavidS-broaden-pick-arguments2'

* DavidS-broaden-pick-arguments2:
  (PUP-638) Add a pick_default() function that always returns a value.
  (PUP-636) Ignore generated file