malloc changes

[Kevin L. Kane]

OpenBSD has alot of useful changes to its malloc.c so I decided to
pull over a bunch of that.

fetch http://www.uberstyle.net/malloc.patch

patch includes:
guard pages and chunk randomization
free page protection
malloc stats(dump)
pointer guard
no longer uses brk/sbrk
updated man page

affects the following files:
lib/libc/stdlib/malloc.c
lib/libc/stdlib/malloc.3
lib/libc/gen/err.c

in err.c i had to weak symbol warn.  if you dont do that after you
compile and install the patched libc it will fail make buildworld in
lex.

-Kevin