Fix fencepost error with HearbeatPeriod option

We'd only log every HeartbeatPeriod + 1 seconds. Discovered by Scott
Bennett, reported as bug 4942.

changes/bug4942

@@ -0,0 +1,5 @@
+  o Minor bugfixes:
+    - Actually log the heartbeat message every HeartbeatPeriod seconds, not
+      every HeartbeatPeriod + 1 seconds. Fixes bug 4942; bugfix on
+      0.2.3.1-alpha.. Bug reported by Scott Bennett.
+

src/or/main.c

@@ -1533,7 +1533,7 @@ run_scheduled_events(time_t now)
 
   /** 12. write the heartbeat message */
   if (options->HeartbeatPeriod &&
-      time_to_next_heartbeat < now) {
+      time_to_next_heartbeat <= now) {
     log_heartbeat(now);
     time_to_next_heartbeat = now+options->HeartbeatPeriod;
   }