Windows compile fixups (To be verified by respective devs)

sql/field.cc:
  Windows - Cast (longlong -> uint)
sql/item_uniq.h:
  Windows compile fix
sql/sql_derived.cc:
  Windows - compile fix

sql/field.cc

@@ -1913,7 +1913,7 @@ int Field_longlong::store(const char *from,uint len,CHARSET_INFO *cs)
   char *end;
   
   tmp= cs->scan(cs, from, from+len, MY_SEQ_SPACES);
-  len-= tmp;
+  len-= (uint)tmp;
   from+= tmp;
   my_errno=0;
   if (unsigned_flag)

sql/item_uniq.h

@@ -50,7 +50,7 @@ public:
     fixed= 1;
     return 0;
   }
-  Item_sum *copy_or_same(THD* thd)
+  Item *copy_or_same(THD* thd)
   {
     return new Item_sum_unique_users(thd, *this);
   }

sql/sql_derived.cc

@@ -71,7 +71,7 @@ int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
   TABLE_LIST *tables= (TABLE_LIST *)sl->table_list.first;
   TMP_TABLE_PARAM tmp_table_param;
   bool is_union= sl->next_select() && sl->next_select()->linkage == UNION_TYPE;
-  bool is_subsel= sl->first_inner_unit();
+  bool is_subsel= sl->first_inner_unit() ? 1: 0;
   SELECT_LEX_NODE *save_current_select= lex->current_select;
   DBUG_ENTER("mysql_derived");