Changed mysql-test to print warnings for not existing table to DROP TABLE

Cleaned up test; Removed wrong DROP TABLE commands and use standard table and database names.
changed store_warning() -> push_warning_print()

mysql-test/t/func_isnull.test

@@ -2,7 +2,10 @@
 # test of ISNULL()
 #
 
+--disable_warnings
 drop table if exists t1;
+--enable_warnings
+
 create table t1 (id int auto_increment primary key not null, mydate date not null);
 insert into t1 values (0,"2002-05-01"),(0,"2002-05-01"),(0,"2002-05-01");
 flush tables;