fix for bug #14381 (Key length is limited to 255 bytes on BDB)

sql/ha_berkeley.h:
  BDB supports keylength of maximal 2^32 - use the maximum allowed by mysqld.
  (http://www.sleepycat.com/docs/ref/am_misc/dbsizes.html)

sql/ha_berkeley.h

@@ -94,6 +94,9 @@ class ha_berkeley: public handler
   uint max_supported_keys()        const { return MAX_KEY-1; }
   uint extra_rec_buf_length()	 { return BDB_HIDDEN_PRIMARY_KEY_LENGTH; }
   ha_rows estimate_rows_upper_bound();
+  uint max_supported_key_length() const { return MAX_KEY_LENGTH; }
+  uint max_supported_key_part_length() const { return MAX_KEY_LENGTH; }
+
   const key_map *keys_to_use_for_scanning() { return &key_map_full; }
   bool has_transactions()  { return 1;}