Split of architecture-dependent and -independent functions for i386,

mainly in the kernel and headers. This split based on work by
Ingmar Alting <iaalting@cs.vu.nl> done for his Minix PowerPC architecture
port.

 . kernel does not program the interrupt controller directly, do any
   other architecture-dependent operations, or contain assembly any more,
   but uses architecture-dependent functions in arch/$(ARCH)/.
 . architecture-dependent constants and types defined in arch/$(ARCH)/include.
 . <ibm/portio.h> moved to <minix/portio.h>, as they have become, for now,
   architecture-independent functions.
 . int86, sdevio, readbios, and iopenable are now i386-specific kernel calls
   and live in arch/i386/do_* now.
 . i386 arch now supports even less 86 code; e.g. mpx86.s and klib86.s have
   gone, and 'machine.protected' is gone (and always taken to be 1 in i386).
   If 86 support is to return, it should be a new architecture.
 . prototypes for the architecture-dependent functions defined in
   kernel/arch/$(ARCH)/*.c but used in kernel/ are in kernel/proto.h
 . /etc/make.conf included in makefiles and shell scripts that need to
   know the building architecture; it defines ARCH=<arch>, currently only
   i386.
 . some basic per-architecture build support outside of the kernel (lib)
 . in clock.c, only dequeue a process if it was ready
 . fixes for new include files

files deleted:
 . mpx/klib.s - only for choosing between mpx/klib86 and -386
 . klib86.s - only for 86

i386-specific files files moved (or arch-dependent stuff moved) to arch/i386/:
 . mpx386.s (entry point)
 . klib386.s
 . sconst.h
 . exception.c
 . protect.c
 . protect.h
 . i8269.c

kernel/system/do_nice.c

@@ -30,7 +30,7 @@ PUBLIC int do_nice(message *m_ptr)
   if (pri == PRIO_STOP) {
 
       /* Take process off the scheduling queues. */
-      lock_dequeue(rp);
+      if(rp->p_rts_flags == 0) lock_dequeue(rp);
       rp->p_rts_flags |= NO_PRIORITY;
       return(OK);
   }
@@ -48,7 +48,7 @@ PUBLIC int do_nice(message *m_ptr)
       /* Make sure the process is not running while changing its priority. 
        * Put the process back in its new queue if it is runnable.
        */
-      lock_dequeue(rp);
+      if(rp->p_rts_flags == 0) lock_dequeue(rp);
       rp->p_rts_flags &= ~NO_PRIORITY;
       rp->p_max_priority = rp->p_priority = new_q;
       if (! rp->p_rts_flags) lock_enqueue(rp);