Use more portable random seed generation.

The new function md_random_seed() has replaced time() + getpid() and
similar methods.  Putting everything in mdport.c slightly reduces the
warnings and workarounds.

xrogue/main.c

@@ -166,7 +166,7 @@ main(int argc, char *argv[], char *envp[])
         seed = atoi(getenv("SEED")); 
     }
     else {
-        seed = (int) time(&now) + getpid();
+        seed = md_random_seed();
     }
     if (wizard)
         printf("Hello %s, welcome to dungeon #%d\n", whoami, seed);