sim: have a curTick per eventq

This patch adds a _curTick variable to an eventq. This variable is updated
whenever an event is serviced in function serviceOne(), or all events upto
a particular time are processed in function serviceEvents(). This change
helps when there are eventqs that do not make use of curTick for scheduling
events.

src/sim/serialize.cc

@@ -465,7 +465,7 @@ Globals::unserialize(Checkpoint *cp, const std::string &section)
 {
     Tick tick;
     paramIn(cp, section, "curTick", tick);
-    curTick(tick);
+    mainEventQueue.setCurTick(tick);
 
     mainEventQueue.unserialize(cp, "MainEventQueue");
 }