avoid deadlock when setting timer in timer event

when using user timers, new timers can now be set and current timers
removed when processing the timer event (i.e. directly in the postEvent
function - which should not be blocking for long time anyway)

core/plug-in/session_timer/UserTimer.cpp

@@ -70,6 +70,8 @@ bool operator < (const AmTimer& l, const AmTimer& r)
 }
 
 void UserTimer::checkTimers() {
+  vector<std::pair<string, int> > expired_timers;
+
   timers_mut.lock();
   if(timers.empty()){
     timers_mut.unlock();
@@ -87,19 +89,26 @@ void UserTimer::checkTimers() {
     string session_id = it->session_id;
     // erase
     timers.erase(it);
-    // 'fire' timer	  
-    if (!AmSessionContainer::instance()->postEvent(session_id, 
-						   new AmTimeoutEvent(id))) {
-      DBG("Timeout Event could not be posted, session does not exist any more.\n");
-    }
-    else {
-      DBG("Timeout Event could be posted.\n");
-    }
+    expired_timers.push_back(make_pair(session_id, id));
     
     if(timers.empty()) break;
     it = timers.begin();
   }
   timers_mut.unlock();
+
+  for (vector<std::pair<string, int> >::iterator e_it =
+	 expired_timers.begin(); e_it != expired_timers.end(); e_it++) {
+    // 'fire' timer
+    if (!AmSessionContainer::instance()->postEvent(e_it->first, 
+						   new AmTimeoutEvent(e_it->second))) {
+      DBG("Timeout Event '%d' could not be posted, session '%s' does not exist any more.\n",
+	  e_it->second, e_it->first.c_str());
+    }
+    else {
+      DBG("Timeout Event '%d' posted to %s.\n", 
+	  e_it->second, e_it->first.c_str());
+    }
+  }
 }
 
 void UserTimer::setTimer(int id, int seconds, const string& session_id) {