replay: checkpoints

This patch introduces checkpoints that synchronize cpu thread and iothread.
When checkpoint is met in the code all asynchronous events from the queue
are executed.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20150917162444.8676.52916.stgit@PASHA-ISP.def.inno>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
diff --git a/stubs/replay.c b/stubs/replay.c
index f0d95b0..3354fcf 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -1,5 +1,6 @@
 #include "sysemu/replay.h"
 #include <stdlib.h>
+#include "sysemu/sysemu.h"
 
 ReplayMode replay_mode;
 
@@ -14,3 +15,8 @@
     abort();
     return 0;
 }
+
+bool replay_checkpoint(ReplayCheckpoint checkpoint)
+{
+    return true;
+}