A little houskeeping.

Increasing counter sizes from int to long for averages.
Rename random functions to end with _co instead of _exclusive to
indicate range [close, open[, and to allow future suffixes oc, cc and oo.

server/modules/routing/readwritesplit/rwsplit_select_backends.cc

@@ -161,7 +161,7 @@ PRWBackends::iterator backend_cmp_response_time(PRWBackends& sBackends)
     }
 
     // Find the winner, role the ball:
-    double ball = maxbase::Worker::get_current()->random_engine().zero_to_one_exclusive();
+    double ball = maxbase::Worker::get_current()->random_engine().zero_to_one_co();
 
     double slot_walk {0};
     int winner {0};