Add a "max_size" parameter to diff_delta()

Anything that generates a delta to see if two objects are close usually
isn't interested in the delta ends up being bigger than some specified
size, and this allows us to stop delta generation early when that
happens.

diffcore-break.c

@@ -65,7 +65,7 @@ static int should_break(struct diff_filespec *src,
 
 	delta = diff_delta(src->data, src->size,
 			   dst->data, dst->size,
-			   &delta_size);
+			   &delta_size, ~0UL);
 
 	/* Estimate the edit size by interpreting delta. */
 	if (count_delta(delta, delta_size,