implement CEILING and FLOOR in terms of %CEILING and %FLOOR

implement CEILING and FLOOR in terms of %CEILING and %FLOOR

  This allows transforms specific to CEILING and FLOOR fire first.

  If they fail, the fallback transforms to %CEILING or %FLOOR,
  respectively.

  They in turn are inlined, allowing the transforms for TRUNCATE
  to pick up the slack.

  This allows the new division -> multiplication transforms to fire
  for CEILING and FLOOR when SPACE > 1.