lot's of fixes with test cases

mysql-test/r/create.result:
  A test case for foreign key bug that is resolved
mysql-test/r/select_found.result:
  test case for new select ... limit 0 behaviour
mysql-test/t/create.test:
  test case for foreign key bug that is fixed
mysql-test/t/select_found.test:
  test case for new behaviour of SELECT ... LIMIT 0
sql/sql_select.cc:
  SELECT ... LIMIT 0
sql/sql_union.cc:
  replacing my dirty hack with Sanja's "proper" fix

mysql-test/r/create.result

@@ -158,3 +158,6 @@ select * from t1;
 if('2002'='2002','Y','N')
 Y
 drop table if exists t1;
+create table t1 (a int, key(a));
+create table t2 (b int, foreign key(b) references t1(a), key(b));
+drop table if exists t1,t2;

mysql-test/r/select_found.result

@@ -173,9 +173,9 @@ SELECT SQL_CALC_FOUND_ROWS 1 FROM (SELECT 1) LIMIT 0;
 SELECT FOUND_ROWS();
 FOUND_ROWS()
 1
-SELECT SQL_CALC_FOUND_ROWS * FROM t1 LIMIT 0;
+SELECT SQL_CALC_FOUND_ROWS * FROM t1 WHERE numeropost > 1  LIMIT 0;
 titre	numeropost	maxnumrep
 SELECT FOUND_ROWS();
 FOUND_ROWS()
-3
+2
 drop table t1;

mysql-test/t/create.test

@@ -110,3 +110,6 @@ drop table t1;
 create table t1 select if('2002'='2002','Y','N');
 select * from t1;
 drop table if exists t1;
+create table t1 (a int, key(a));
+create table t2 (b int, foreign key(b) references t1(a), key(b));
+drop table if exists t1,t2;

mysql-test/t/select_found.test

@@ -86,6 +86,6 @@ SELECT SQL_CALC_FOUND_ROWS titre,numeropost,maxnumrep FROM t1 WHERE numeropost I
 SELECT FOUND_ROWS();
 SELECT SQL_CALC_FOUND_ROWS 1 FROM (SELECT 1) LIMIT 0;
 SELECT FOUND_ROWS();
-SELECT SQL_CALC_FOUND_ROWS * FROM t1 LIMIT 0;
+SELECT SQL_CALC_FOUND_ROWS * FROM t1 WHERE numeropost > 1  LIMIT 0;
 SELECT FOUND_ROWS();
 drop table t1;

sql/sql_select.cc

@@ -324,6 +324,7 @@ JOIN::prepare(TABLE_LIST *tables_init,
   this->group= group_list != 0;
   row_limit= ((select_distinct || order || group_list) ? HA_POS_ERROR :
 	      unit->select_limit_cnt);
+  do_send_rows = (row_limit) ? 1 : 0;
   this->unit= unit;
 
 #ifdef RESTRICTED_GROUP
@@ -664,7 +665,7 @@ JOIN::exec()
       result->send_fields(fields_list,1);
       if (!having || having->val_int())
       {
-	if (do_send_rows && unit->select_limit_cnt && result->send_data(fields_list))
+	if (do_send_rows && result->send_data(fields_list))
 	  error= 1;
 	else
 	{
@@ -2611,8 +2612,8 @@ make_simple_join(JOIN *join,TABLE *tmp_table)
   join->sum_funcs=0;
   join->send_records=(ha_rows) 0;
   join->group=0;
-  join->do_send_rows = 1;
   join->row_limit=join->unit->select_limit_cnt;
+  join->do_send_rows = (join->row_limit) ? 1 : 0;
 
   join_tab->cache.buff=0;			/* No cacheing */
   join_tab->table=tmp_table;
@@ -5184,7 +5185,7 @@ end_send(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
     error=0;
     if (join->procedure)
       error=join->procedure->send_row(*join->fields);
-    else if (join->do_send_rows && join->unit->select_limit_cnt)
+    else if (join->do_send_rows)
       error=join->result->send_data(*join->fields);
     if (error)
       DBUG_RETURN(-1); /* purecov: inspected */

sql/sql_union.cc

@@ -86,7 +86,6 @@ bool select_union::send_data(List<Item> &values)
     }
     else
       return 1;
-    thd->net.report_error=0; // donno why does it work, but it does ...
   }
   return 0;
 }