kmem allocation changes for uvm, and vm_fork -> uvm_fork (with one extra argument)

update the comment about number of allowed processes

Allow up to 5 (was 1) root processes when the process limit is reached.
This gives root a bigger chance to fix any problem that caused the limit
to be reached.

Ooops! Move the allocation of the U area to after the limits checks.
That was a memory leak.

Allocate the u-area early in fork1 instead of in vm_fork.
Now we can return ENOMEM instead of doing a panic when we run out of memory.

just check rforkflags if ISRFORK

Make RFNOWAIT work in rfork(2)

only allow setuid if fd_refcnt == 1, due to rfork

disable RFFDG; long explanation...

count pages in forkstat, see "vmstat -f"

random pid generation, heh

cp P_SUGID/P_SUGIDEXEC to child, doh; half from freebsd

Rename nextpid to lastpid; make it a global with type pid_t

From NetBSD: 960217 merge

Count number of forks, vforks, rforks; still need to count VM pages affected
by the various fork types

plan9-like rfork() implimentation by me based on some earlier incomplete
work by rminnich@Sarnoff.COM. still needs RFNOWAIT support.

from netbsd:
Only expect vm_fork() to return if __FORK_BRAINDAMAGE is defined.
Use splstatclock() rather than splhigh() in one place.
Eliminate unused third arg to vm_fork().

initial import of NetBSD tree