scandir() calls realloc too much and is not pessimistic enuf

[Jay Lepreau]

Index:	lib/libc/gen/scandir.c 4.2BSD Fix

Description:
	1.  If the arraysz estimate proved low, scandir does a realloc
	assuming the worst, but it never recomputes the new arraysz,
	so it keeps calling realloc all the rest of the way thru the dir.
	(This isn't as bad as it sounds, for realloc is smart enuf not
	to do anything if the same size is requested.)
	2. scandir is overly optimistic about the worst case: the directory
	could grow on it (unless there's some synchrony out there I don't
	know about), leading to an infinite loop.  It should restat the
	directory.
Repeat-By:
	Well, *I* noticed it from that nifty gprof output showing
	hundreds of realloc calls.  Obvious from inspection too.
Fix:
***************
*** 60,61
  		if (++nitems >= arraysz) {
  			names = (struct direct **)realloc((char *)names,

--- 62,66 -----
  		if (++nitems >= arraysz) {
+ 			if (fstat(dirp->dd_fd, &stb) < 0)
+ 				return(-1);	/* just might have grown */
+ 			arraysz = stb.st_size/12;
  			names = (struct direct **)realloc((char *)names,
***************
*** 61,63
  			names = (struct direct **)realloc((char *)names,
! 				(stb.st_size/12) * sizeof(struct direct *));
  			if (names == NULL)

--- 66,68 -----
  			names = (struct direct **)realloc((char *)names,
! 				arraysz * sizeof(struct direct *));
  			if (names == NULL)