improve warnings from rand_r(), rand(), and random()

It may take a few iterations to get the tone right.
previously discussed with millert

src/lib/libc/stdlib/rand.c

@@ -42,7 +42,7 @@ rand_r(u_int *seed)
 
 #if defined(APIWARN)
 __warn_references(rand_r,
-    "warning: rand_r() isn't random; consider using arc4random()");
+    "warning: rand_r() is not random, it is deterministic.");
 #endif
 
 int
@@ -55,7 +55,7 @@ rand(void)
 
 #if defined(APIWARN)
 __warn_references(rand,
-    "warning: rand() isn't random; consider using arc4random()");
+    "warning: rand() may return determinstic values, is that what you want?");
 #endif
 
 void

src/lib/libc/stdlib/random.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: random.c,v 1.25 2014/12/08 21:45:20 deraadt Exp $ */
+/*	$OpenBSD: random.c,v 1.26 2014/12/09 08:00:53 deraadt Exp $ */
 /*
  * Copyright (c) 1983 Regents of the University of California.
  * All rights reserved.
@@ -415,3 +415,8 @@ random(void)
 	UNLOCK();
 	return r;
 }
+
+#if defined(APIWARN)
+__warn_references(rand,
+    "warning: random() may return determinstic values, is that what you want?");
+#endif