use boxed constants for full calls

use boxed constants for full calls

 If a constant is being used in a full call, use a boxed representation
 instead of an inline one which must then be boxed at runtime.  Also arrange
 to have both an immediate unboxed and a boxed representation when
 advantageous.

 (There might be other cases besides full calls where we should prefer boxed
 representations, but that's for later.)