Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

- Removing some unneeded definitions of NULL(cruft related to 1970's C).
In C90, NULL is guaranteed to be declared in <stddef.h> and also in
<string.h>. Though the correct way to define NULL in FreeBSD is to
include <sys/_null.h>, other parts of libstand still require <string.h>
to build; therefore, we keep <string.h> in stand.h and add a note about
this;
- Removing no longer used 'Prototype' definition. Quote from bde@:

'Cruft related to getting incomplete struct declarations within
prototypes forward-declared before the structs. It doesn't mean
"prototype" but only part of a prototype-related hack. No longer
used.'

- Replacing iaddr_t with uintptr_t;
- Removing use of long double to determine alignment. Use a fixed 16 byte
alignment instead;

Reviewed by: bde
Obtained from: DragonFlyBSD (partially)
MFC after: 1 month

$Id$ -> $FreeBSD$

Prune unused zalloc components as recommended by Matt Dillon. Extra debugging
code is still enabled (it's not very expensive).

Replace the old and extremely icky Mach/NetBSD allocator with a similarly
compact and much better one donated by Matt Dillon. Implement a simple
sbrk() which uses the existing setheap() api.

Remove the custom allocator from the UFS code. It wasn't working quite
right, and it shouldn't be needed with the new allocator.

Fix a serious problem with changing the value of already-existent
environment variables. Don't attempt to modify the supposedly-const
argument to putenv()

Fix an off-by-one sizing error in the zipfs code detected by the new
allocator.

Submitted by: zmalloc from Matt Dillon <dillon@backplane.com>