unnecessary {de,}alloc wrappers?

[Ondrej Oprala]

Hi,
 Could someone please explain to me, why are xrealloc and xfree (or 
more specifically - their parts) from lib/malloc/xmalloc.c necessary?

e.g.
if (string)
    free(string);
Why is this needed? AFAIK the C standard specifies free(NULL) is 
completely legal.
Also:
  temp = pointer ? realloc (pointer, bytes) : malloc (bytes);
Again, the C standard says that realloc(0, bytes) is equivalent to 
malloc(bytes).
So why check for these cases?

Thanks,
Ondrej