after discussion with ciruZ, switch mksh from NZAT to NZAAT fully

to get rid of the bias introduced by making the hash never zero

… he also pointed out a memory (heap) usage optimisation… which
may impact code size a bit though as I’d need to pass an additional
argument on hashtable function calls… or, forgo the benefit of not
having to pointer-align the key in the structure, which can be as
much as 3/7 octets per item, heap storage… OTOH the saved space is
4/8 octets per not-allocated item, possibly some code (use of an
multiply-add opcode), but the function call overhead/cost would
possibly be quite a bit… I guess I’ll have to measure…

var.c

@@ -27,7 +27,7 @@
 #include <sys/sysctl.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/var.c,v 1.146 2012/04/14 14:35:13 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/var.c,v 1.147 2012/04/22 21:50:35 tg Exp $");
 
 /*-
  * Variables
@@ -1471,7 +1471,7 @@ hash(const void *s)
 
 	NZATInit(h);
 	NZATUpdateString(h, s);
-	NZATFinish(h);
+	NZAATFinish(h);
 	return (h);
 }