Merge of David's ptrace branch. Summary:

o Support for ptrace T_ATTACH/T_DETACH and T_SYSCALL
o PM signal handling logic should now work properly, even with debuggers
  being present
o Asynchronous PM/VFS protocol, full IPC support for senda(), and
  AMF_NOREPLY senda() flag

DETAILS

Process stop and delay call handling of PM:
o Added sys_runctl() kernel call with sys_stop() and sys_resume()
  aliases, for PM to stop and resume a process
o Added exception for sending/syscall-traced processes to sys_runctl(),
  and matching SIGKREADY pseudo-signal to PM
o Fixed PM signal logic to deal with requests from a process after
  stopping it (so-called "delay calls"), using the SIGKREADY facility
o Fixed various PM panics due to race conditions with delay calls versus
  VFS calls
o Removed special PRIO_STOP priority value
o Added SYS_LOCK RTS kernel flag, to stop an individual process from
  running while modifying its process structure

Signal and debugger handling in PM:
o Fixed debugger signals being dropped if a second signal arrives when
  the debugger has not retrieved the first one
o Fixed debugger signals being sent to the debugger more than once
o Fixed debugger signals unpausing process in VFS; removed PM_UNPAUSE_TR
  protocol message
o Detached debugger signals from general signal logic and from being
  blocked on VFS calls, meaning that even VFS can now be traced
o Fixed debugger being unable to receive more than one pending signal in
  one process stop
o Fixed signal delivery being delayed needlessly when multiple signals
  are pending
o Fixed wait test for tracer, which was returning for children that were
  not waited for
o Removed second parallel pending call from PM to VFS for any process
o Fixed process becoming runnable between exec() and debugger trap
o Added support for notifying the debugger before the parent when a
  debugged child exits
o Fixed debugger death causing child to remain stopped forever
o Fixed consistently incorrect use of _NSIG

Extensions to ptrace():
o Added T_ATTACH and T_DETACH ptrace request, to attach and detach a
  debugger to and from a process
o Added T_SYSCALL ptrace request, to trace system calls
o Added T_SETOPT ptrace request, to set trace options
o Added TO_TRACEFORK trace option, to attach automatically to children
  of a traced process
o Added TO_ALTEXEC trace option, to send SIGSTOP instead of SIGTRAP upon
  a successful exec() of the tracee
o Extended T_GETUSER ptrace support to allow retrieving a process's priv
  structure
o Removed T_STOP ptrace request again, as it does not help implementing
  debuggers properly
o Added MINIX3-specific ptrace test (test42)
o Added proper manual page for ptrace(2)

Asynchronous PM/VFS interface:
o Fixed asynchronous messages not being checked when receive() is called
  with an endpoint other than ANY
o Added AMF_NOREPLY senda() flag, preventing such messages from
  satisfying the receive part of a sendrec()
o Added asynsend3() that takes optional flags; asynsend() is now a
  #define passing in 0 as third parameter
o Made PM/VFS protocol asynchronous; reintroduced tell_fs()
o Made PM_BASE request/reply number range unique
o Hacked in a horrible temporary workaround into RS to deal with newly
  revealed RS-PM-VFS race condition triangle until VFS is asynchronous

System signal handling:
o Fixed shutdown logic of device drivers; removed old SIGKSTOP signal
o Removed is-superuser check from PM's do_procstat() (aka getsigset())
o Added sigset macros to allow system processes to deal with the full
  signal set, rather than just the POSIX subset

Miscellaneous PM fixes:
o Split do_getset into do_get and do_set, merging common code and making
  structure clearer
o Fixed setpriority() being able to put to sleep processes using an
  invalid parameter, or revive zombie processes
o Made find_proc() global; removed obsolete proc_from_pid()
o Cleanup here and there

Also included:
o Fixed false-positive boot order kernel warning
o Removed last traces of old NOTIFY_FROM code

THINGS OF POSSIBLE INTEREST

o It should now be possible to run PM at any priority, even lower than
  user processes
o No assumptions are made about communication speed between PM and VFS,
  although communication must be FIFO
o A debugger will now receive incoming debuggee signals at kill time
  only; the process may not yet be fully stopped
o A first step has been made towards making the SYSTEM task preemptible

drivers/audio/framework/audio_fw.c

@@ -44,6 +44,7 @@
 
 #include "audio_fw.h"
 #include <sys/vm.h>
+#include <minix/endpoint.h>
 #include <minix/ds.h>
 #include <sys/vm_i386.h>
 
@@ -92,14 +93,29 @@ PUBLIC void main(void)
 		caller = mess.m_source;
 		proc_nr = mess.IO_ENDPT;
 
-		if (caller == RS_PROC_NR && mess.m_type == DEV_PING)
-		{
-			/* Got ping from RS. Just notify RS */
-			notify(RS_PROC_NR);
+		/* Now carry out the work. First check for notifications. */
+		if (is_notify(mess.m_type)) {
+			switch (_ENDPOINT_P(mess.m_source)) {
+				case HARDWARE:
+					msg_hardware();
+					break;
+				case PM_PROC_NR:
+					msg_sig_stop();
+					break;
+				case RS_PROC_NR:
+					/* Got ping from RS. Just notify RS */
+					notify(RS_PROC_NR);
+					break;
+				default:
+					dprint("%s: %d uncaught notify!\n",
+						drv.DriverName, mess.m_type);
+			}
+
+			/* get next message */
 			continue;
 		}
 
-		/* Now carry out the work. */
+		/* Normal messages. */
 		switch(mess.m_type) {
 			case DEV_OPEN:
 				/* open the special file ( = parameter) */
@@ -149,10 +165,6 @@ PUBLIC void main(void)
 				repl_mess.REP_STATUS = r;
 				send(caller, &repl_mess);
 				continue;
-			case HARD_INT:
-				msg_hardware();continue;  /* don't reply */
-			case SYS_SIG:		  
-				msg_sig_stop(); continue; /* don't reply */
 			default:          
 				dprint("%s: %d uncaught msg!\n",
 					drv.DriverName, mess.m_type);
@@ -883,14 +895,14 @@ PRIVATE int init_buffers(sub_dev_t *sub_dev_ptr)
 {
 #if (CHIP == INTEL)
 	char *base;
-	size_t size, off;
+	size_t size;
 	unsigned left;
 	u32_t i;
 	phys_bytes ph;
 
 	/* allocate dma buffer space */
 	size= sub_dev_ptr->DmaSize + 64 * 1024;
-	off = base= alloc_contig(size, AC_ALIGN4K, &ph);
+	base= alloc_contig(size, AC_ALIGN4K, &ph);
 	if (!base) {
 		error("%s: failed to allocate dma buffer for channel %d\n", 
 				drv.DriverName,i);