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/state.c

@@ -3619,3 +3619,16 @@ md_unlink(char *file)
     return(unlink(file));
 #endif
 }
+
+unsigned int
+md_random_seed(void)
+{
+    unsigned int seed;
+    seed = (unsigned int) time((time_t *) NULL);
+#ifdef _WIN32
+    seed += _getpid();
+#else
+    seed += getpid();
+#endif
+    return seed;
+}