WL#3700: Handler API change: all index search methods - that is,

index_read(), index_read_idx(), index_read_last(), and
records_in_range() - instead of 'uint keylen' argument take
'ulonglong keypart_map', a bitmap showing which keyparts are
present in the key value.
Fallback method is provided for handlers that are lagging behind.

storage/example/ha_example.h

@@ -191,7 +191,7 @@ public:
     skip it and and MySQL will treat it as not implemented.
   */
   int index_read(byte * buf, const byte * key,
-                 uint key_len, enum ha_rkey_function find_flag);
+                 ulonglong keypart_map, enum ha_rkey_function find_flag);
 
   /** @brief
     We implement this in ha_example.cc. It's not an obligatory method;