Add the sqlite3_log_hook() interface for scheduling checkpoints.

FossilOrigin-Name: 9bda601455705475075e33bfa85687bce34b15ff
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 6007b8a..1dfc86d 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -823,6 +823,8 @@
   void (*xRollbackCallback)(void*); /* Invoked at every commit. */
   void *pUpdateArg;
   void (*xUpdateCallback)(void*,int, const char*,const char*,sqlite_int64);
+  int (*xLogCallback)(void *, sqlite3 *, const char *, u32);
+  void *pLogArg;
   void(*xCollNeeded)(void*,sqlite3*,int eTextRep,const char*);
   void(*xCollNeeded16)(void*,sqlite3*,int eTextRep,const void*);
   void *pCollNeededArg;