#8 Check downloaded files for updates

[blackboxxx]

Many download managers (e.g., FlashGet) implement a feature that allows to check downloaded files for updates.

When this option is selected, current size and timestamp are retrieved from the server, and if they don't match with the previously downloaded file, the file is downloaded again.

This is useful to monitor for software updates (including new builds of FDM itself), get the latest definitions for antivirus/antispyware, etc.