Downward interfaces

The downward interfaces we used in our component include:

• Status BufMgr::newPage(PageId, Page*&, int = 1)
• Status BufMgr::freePage(PageId)
• Status BufMgr::pinPage(PageId, Page*&)
• Status BufMgr::unpinPage(PageId,DIRTY_FLAG)
• Status DB::add_file_entry(const char*, PageId);
• Status DB::get_file_entry(const char*, PageId);
• Status DB::delete_file_entry(const char*, PageId);
• Status RecoveryMgr::WriteUpdateLog(int,PageId,int,void*,void*,Page*)
• Status lock_manager_def::lock_page(page_def,lock_type)
• Status lock_manager_def::unlock_page(page_def)
• Status lock_manager_def::upgrade_lock(page_def,lock_type)
• the constructors and destructors for the above classes