Fix ghost threads in CPU

* kernel: Make sf9 return TSTATE_FREE for invalid slots: 0, >255, free.
* menu: Ignore free slots even if other fields of proc_info look valid.
        Documentation (sysfuncs.txt) clearly states all the other info
        as invalid when slot_state is TSTATE_FREE.
* taskbar: Same as menu.
* cmm/lib/*: Same as menu.
* programs/macros.inc: Add TSTATE_* macros.

programs/system/menu/trunk/menu.asm

@@ -783,13 +783,14 @@ align 4
 .loop:
 	push	ecx
 	mcall	9,procinfo
+        cmp     word[ebx+50], TSTATE_FREE
+        je      @f
 	mov	eax,[menu_mame]
 	cmp	[ebx+10],eax
 	jne	@f
-	; temporary to fit into 3 IMG sectors
-	;mov	ax,[menu_mame+4]
-	;cmp	[ebx+14],ax
-	;jne	@f
+	mov	ax,[menu_mame+4]
+	cmp	[ebx+14],ax
+	jne	@f
 	cmp	ecx,[active_process]
 	je	@f
 ; dph ecx