SERVER-8487 Fix broken condition in oplog reader code.

Author: erh

src/mongo/db/oplog.cpp

@@ -100,6 +100,8 @@ namespace mongo {
                 ctx.getClient()->setLastOp( ts );
             }
         }
+
+        OpTime::setLast( ts );
     }
 
     /** given a BSON object, create a new one at dst which is the existing (partial) object

src/mongo/util/optime.h

@@ -42,9 +42,15 @@ namespace mongo {
     public:
         static void setLast(const Date_t &date) {
             mutex::scoped_lock lk(m);
-            notifier.notify_all(); // won't really do anything until write-lock released
             last = OpTime(date);
+            notifier.notify_all();
         }
+        static void setLast(const OpTime &new_last) {
+            mutex::scoped_lock lk(m);
+            last = new_last;
+            notifier.notify_all();
+        }
+
         unsigned getSecs() const {
             return secs;
         }