Fix for Bug#3759

The cause of the bug is that Item_func_in::fix_fields did not fully update its
used_table_cache. This was the cause for not_null_tables in setup_conds() to be
still 0 after the call
  not_null_tables= (*conds)->not_null_tables();
As a result the condition in setup_conds()
  if ( ... (table->table->map & not_null_tables) ...)
failed, which was the cause for the ON expression not to be added to conds, and later
the optimizer couldn't detect that it could apply the OUTER JOIN ==> JOIN optimization.

BitKeeper/etc/logging_ok

@@ -136,6 +136,7 @@ tim@sand.box
 tim@threads.polyesthetic.msg
 tim@white.box
 tim@work.mysql.com
+timour@mysql.com
 tom@basil-firewall.home.com
 tonu@hundin.mysql.fi
 tonu@volk.internalnet

sql/item_cmpfunc.h

@@ -431,6 +431,9 @@ class Item_func_in :public Item_int_func
   {
     bool res=  (item->fix_fields(thd,tlist) || Item_func::fix_fields(thd,tlist));
     with_sum_func= with_sum_func || item->with_sum_func;
+    used_tables_cache|=     item->used_tables();
+    not_null_tables_cache|= item->not_null_tables();
+    const_item_cache&=      item->const_item();
     return res; 
   }
   void fix_length_and_dec();