* Fix a number of cases where too much kernel memory might be allocated to

* Fix a number of cases where too much kernel memory might be allocated to
  satisfy a directory read operation.

* Calculate a minimum of (1) allocated directory cookie and limit the maximum
  to 1024.

* Rewrite ufs_readdir() (part 1/2) to use the buffer cache instead of
  allocating a kernel buffer and to do better validation of the scanned
  directory entries.

* Use a simpler fix for EXT2FS.

Reported-by: [NetBSD.org #7471]