Fix for bug #8143: A date with value 0 is treated as a NULL value

mysql-test/r/delete.result:
  Fix for bug #8143: A date with value 0 is treated as a NULL value
    - test result
mysql-test/t/delete.test:
  Fix for bug #8143: A date with value 0 is treated as a NULL value
    - test case
sql/sql_delete.cc:
  Fix for bug #8143: A date with value 0 is treated as a NULL value
    - during SELECT queries processing we convert 'date[time]_field is null' 
      conditions into 'date[time]_field = 0000-00-00[ 00:00:00]' for not null 
      DATE and DATETIME fields. To be consistent, we have to do the same for DELETE
      queries. So we should call remove_eq_conds() in the mysql_delete() as well.
      Also it may simplify and speed up DELETE queries execution.

mysql-test/r/delete.result

@@ -192,3 +192,13 @@ delete t2.*,t3.* from t1,t2,t3 where t1.a=t2.a AND t2.b=t3.a and t1.b=t3.b;
 select * from t3;
 a	b
 drop table t1,t2,t3;
+create table t1(a date not null);
+insert into t1 values (0);
+select * from t1 where a is null;
+a
+0000-00-00
+delete from t1 where a is null;
+select count(*) from t1;
+count(*)
+0
+drop table t1;

mysql-test/t/delete.test

@@ -171,3 +171,14 @@ delete t2.*,t3.* from t1,t2,t3 where t1.a=t2.a AND t2.b=t3.a and t1.b=t3.b;
 # This should be empty
 select * from t3;
 drop table t1,t2,t3;
+
+#
+# Bug #8143: deleting '0000-00-00' values using IS NULL
+#
+
+create table t1(a date not null);
+insert into t1 values (0);
+select * from t1 where a is null;
+delete from t1 where a is null;
+select count(*) from t1;
+drop table t1;

sql/sql_delete.cc

@@ -91,6 +91,14 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     /* Handler didn't support fast delete; Delete rows one by one */
   }
 
+  if (conds)
+  {
+    Item::cond_result result;
+    conds= remove_eq_conds(thd, conds, &result);
+    if (result == Item::COND_FALSE)             // Impossible where
+      limit= 0;
+  }
+
   table->used_keys.clear_all();
   table->quick_keys.clear_all();		// Can't use 'only index'
   select=make_select(table, 0, 0, conds, 0, &error);