Removed need for storage engines to write a default external_lock() call.

sql/examples/ha_archive.cc:
  Removed external_lock call (no longer needed, we can now use the default).
sql/examples/ha_archive.h:
  No need for an external_lock() call.
sql/handler.h:
  Added default return value for external_lock().

sql/examples/ha_archive.cc

@@ -828,15 +828,6 @@ int ha_archive::optimize(THD* thd, HA_CHECK_OPT* check_opt)
 }
 
 
-/*
-  No transactions yet, so this is pretty dull.
-*/
-int ha_archive::external_lock(THD *thd, int lock_type)
-{
-  DBUG_ENTER("ha_archive::external_lock");
-  DBUG_RETURN(0);
-}
-
 /* 
   Below is an example of how to setup row level locking.
 */

sql/examples/ha_archive.h

@@ -96,7 +96,6 @@ public:
   int write_data_header(gzFile file_to_write);
   void position(const byte *record);
   void info(uint);
-  int external_lock(THD *thd, int lock_type);
   int create(const char *name, TABLE *form, HA_CREATE_INFO *create_info);
   int optimize(THD* thd, HA_CHECK_OPT* check_opt);
   void start_bulk_insert(ha_rows rows);

sql/handler.h

@@ -449,7 +449,7 @@ public:
   virtual int extra_opt(enum ha_extra_function operation, ulong cache_size)
   { return extra(operation); }
   virtual int reset() { return extra(HA_EXTRA_RESET); }
-  virtual int external_lock(THD *thd, int lock_type)=0;
+  virtual int external_lock(THD *thd, int lock_type) { return 0; }
   virtual void unlock_row() {}
   virtual int start_stmt(THD *thd) {return 0;}
   /*