[Nickle] Removed archaic "v" printing and scanning functions; buglet remains

[Bart Massey]

After talking over with Keith, I concluded that vfprintf(),
vfscanf(), and friends are no longer particularly useful in
Nickle.  The new syntax for expanding arguments does the
same job.  So I removed the "v" functions.

This is not quite a backward-compatible change.  If you had
code that looked like

   void myfn(string fmt, poly args ...) {
     vprintf(fmt, args);
   }

you now need to modify it to look like

   void myfn(string fmt, poly args ...) {
     printf(fmt, args ...);
   }

This is easier to read, and avoids some maintenance
problems.


Sadly, there appears to be a slight prettyprinting buglet
left.  Try invoking
  abort("%d", 1)
at the command line, and notice that in some parts of the
stack trace the second argument is elided.

	Bart