Revert "Un-taint the base tag with "./" things :)"

This reverts commit 0bc5a56ab751f5a6c98f1ebca4df8964207e99ae.
Revert "Remove the filename from BASE_HREF (used for <base />), fixes bug#66138"

This reverts commit cc3a7dccac0b1723b2778414aea89cde1c62e506.
Download system tweaks

Remove reduntant/duplicate code between do-download and get-download

Also make this page more interesting when the download is missing from
this specific mirror by give the choise of going to other mirrors to check.
Rather then blindly go to the download file though we go to the same page
on the other mirror so we can check if the file exists there before giving
the link to the actual real file.

This also makes it a lot easier to work with on developers checkouts