Proposed fix for #751

Fields in key_expr (mysql_ha_read) wasn't linked to tables.
Hmm. How did it work at all?


mysql-test/r/alias.result:
  It's better to delete table after the test
mysql-test/r/handler.result:
  appropriate result
mysql-test/t/alias.test:
  it's better to drop table after test
mysql-test/t/handler.test:
  test case for #751
sql/sql_handler.cc:
  fix_fields called

mysql-test/r/handler.result

@@ -146,3 +146,9 @@ alter table t1 type=MyISAM;
 handler t2 read first;
 Unknown table 't2' in HANDLER
 drop table t1;
+create table t1(a int, index(a));
+insert into t1 values (1), (2), (3);
+handler t1 open;
+handler t1 read a=(W);
+Unknown column 'W' in 'field list'
+drop table t1;