delete agent from the request, if we are going to serialise it.

lib/scheduler.js

@@ -94,7 +94,14 @@ exports.TimerScheduler = TimerScheduler;
         }
       }
       delete state.nextRequest;
+
+      // Using a request object may mutate it; and in particular, may
+      // mutate it into a cyclical structure. As a hack, we make sure
+      // it doesn't have the bit that could be circular. Better might
+      // be to create a fresh request.      
+
       var req = PROTOCOLS[request.protocol].get(request, function(res) {
+        delete request.agent;
         var status = res.statusCode;
 
         // be optimistic
@@ -117,6 +124,7 @@ exports.TimerScheduler = TimerScheduler;
                 state.request.headers = state.request.headers || {};
                 state.lastModified = res.headers['last-modified'];
               }
+
               ok(state);
               // %%%FIXME Perhaps not most efficient. Benchmark? Also,
               // do I really want to assume utf8, or just forward