Added new status variables to make it easier to debug certain problems:

- Handler_read_retry
- Update_scan
- Delete_scan

sql/handler.h

@@ -3090,6 +3090,7 @@ public:
     If this method returns nonzero, it will also signal the storage
     engine that the next read will be a locking re-read of the row.
   */
+  bool ha_was_semi_consistent_read();
   virtual bool was_semi_consistent_read() { return 0; }
   /**
     Tell the engine whether it should avoid unnecessary lock waits.