Fix replace bug w/ BDB tables by passing key_length to index_read_idx.

mysql-test/t/replace.test:
  - test replace with an extra row that has a higher key value
sql/sql_insert.cc:
  - pass real key length to index_read_idx, instead of relying on the
    table handler to convert 0 -> key_length (fixes replace bug in BDB)

mysql-test/t/replace.test

@@ -10,6 +10,7 @@ CREATE TABLE t1 (
   PRIMARY KEY (gesuchnr,benutzer_id)
 ) type=ISAM;
 
+replace into t1 (gesuchnr,benutzer_id) values (2,1);
 replace into t1 (gesuchnr,benutzer_id) values (1,1);
 replace into t1 (gesuchnr,benutzer_id) values (1,1);
 alter table t1 type=myisam;

sql/sql_insert.cc

@@ -366,7 +366,8 @@ int write_record(TABLE *table,COPY_INFO *info)
 	}
 	key_copy((byte*) key,table,key_nr,0);
 	if ((error=(table->file->index_read_idx(table->record[1],key_nr,
-						(byte*) key,0,
+						(byte*) key,
+						table->key_info[key_nr].key_length,
 						HA_READ_KEY_EXACT))))
 	  goto err;
       }