set max vol replica to MIN(count(oldnodes), count(newnodes))
First working single_download version.

If multi_download fails, single_download() is called. It bases on
previous HTTP request statuses. If not correctly downloaded (e.g. 404), blocks are being
retried sequentially.
Revert "spam boost - revert me!!!"

This reverts commit 8b46b1224067778a137610c68aefc34bbe96bed6.
Remove retry logic from multi_download
Fix indentaion in multi_download

This commit changes only indentation. Do not blame for this one.
single_download cosmetics