Simpler arena swapping code

Now thd->mem_root is a pointer to thd->main_mem_root and THR_MALLOC is a pointer to thd->mem_root.
This gives us the following benefits:
- Allow us to easily detect if arena has already been swapped before (this fixes a bug in setup_conds() where arena was swaped twice in some cases)
- Faster swaps of arenas (as we don't have to copy the whole MEM_ROOT)
- We don't anymore have to call my_pthread_setspecific_ptr(THR_MALLOC,...) to change where memory is alloced. Now it's enough to set thd->mem_root



client/mysqltest.c:
  Remove some not needed defines
  (Things like this should be done in config-win.h)
include/config-win.h:
  Added popen() and pclose() compatibility macros
mysql-test/t/rpl_failed_optimize-master.opt:
  Portability fix
sql/ha_berkeley.cc:
  New thd->memroot handling
sql/item_cmpfunc.cc:
  Simpler arena swapping code
sql/item_func.cc:
  Simpler arena swapping code
sql/item_subselect.cc:
  Simpler arena swapping code
  New thd->mem_root handling
sql/item_sum.cc:
  New thd->mem_root handling
sql/item_timefunc.cc:
  Fixed not-initalized usage errors found by valgrind
sql/log_event.cc:
  New thd->mem_root handling
sql/mysql_priv.h:
  New thd->mem_root handling
sql/mysqld.cc:
  New thd->mem_root handling
sql/opt_range.cc:
  New thd->mem_root handling
sql/repl_failsafe.cc:
  New thd->mem_root handling
sql/set_var.cc:
  New thd->mem_root handling
sql/sql_acl.cc:
  New thd->mem_root handling
sql/sql_base.cc:
  Simpler arena swapping code
  New thd->mem_root handling
sql/sql_class.cc:
  New thd->mem_root handling
sql/sql_class.h:
  Simpler arena swapping code
  New thd->mem_root handling
sql/sql_db.cc:
  New thd->mem_root handling
sql/sql_error.cc:
  New thd->mem_root handling
sql/sql_help.cc:
  New thd->mem_root handling
sql/sql_insert.cc:
  New thd->mem_root handling
sql/sql_parse.cc:
  New thd->mem_root handling
  Added some extra checking of return value of new
sql/sql_prepare.cc:
  New thd->mem_root handling
sql/sql_select.cc:
  New thd->mem_root handling
sql/sql_select.h:
  New thd->mem_root handling
sql/sql_union.cc:
  Simpler arena swapping code
sql/sql_yacc.yy:
  New thd->mem_root handling
sql/table.cc:
  New thd->mem_root handling
sql/thr_malloc.cc:
  New thd->mem_root handling
tests/client_test.c:
  Added drop table to some tests
  Changed some table names to 't1'

sql/sql_select.cc

@@ -4603,7 +4603,7 @@ static Field* create_tmp_field_from_field(THD *thd, Field* org_field,
                                    org_field->field_name, table,
                                    org_field->charset());
   else
-    new_field= org_field->new_field(&thd->mem_root, table);
+    new_field= org_field->new_field(thd->mem_root, table);
   if (new_field)
   {
     if (modify_item)
@@ -5206,7 +5206,7 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
       if (!using_unique_constraint)
       {
 	group->buff=(char*) group_buff;
-	if (!(group->field=field->new_field(&thd->mem_root,table)))
+	if (!(group->field=field->new_field(thd->mem_root,table)))
 	  goto err; /* purecov: inspected */
 	if (maybe_null)
 	{
@@ -8499,7 +8499,7 @@ setup_copy_fields(THD *thd, TMP_TABLE_PARAM *param,
 	   saved value
 	*/
 	Field *field= item->field;
-	item->result_field=field->new_field(&thd->mem_root,field->table);
+	item->result_field=field->new_field(thd->mem_root,field->table);
 	char *tmp=(char*) sql_alloc(field->pack_length()+1);
 	if (!tmp)
 	  goto err;
@@ -8942,7 +8942,7 @@ bool JOIN::rollup_init()
     return 1;
   rollup.ref_pointer_arrays= (Item***) (rollup.fields + send_group_parts);
   ref_array= (Item**) (rollup.ref_pointer_arrays+send_group_parts);
-  rollup.item_null= new (&thd->mem_root) Item_null();
+  rollup.item_null= new (thd->mem_root) Item_null();
 
   /*
     Prepare space for field list for the different levels