Generalized path testers.

Many such testers -- particularly those testing non-directory files (e.g.,
:is_file_executable()) -- now accept an arbitrary number of passed paths rather
than merely one.

"This arduous journey malingers,
   indolently inscribed
   of a scurrilous jest
   of a thatched unjustice
   scurrying leeward.

 That stippled centrifuge unduly undulates.

 That well-worn well of ungulate souls,
   indominatably insensate
   in my dominos' lee;
   indubitably, we spent a farthing for
   a Westeros-spittled thimble of
   a westward nihil.

Further on, midnight vigil!
Further in, environs on the sempervirens."