Download sources from servers that don't respond to ping

[Jann Röder]

> I'm still not clear how you ended up with a 0-sized file with obviously
> mismatched checksums if no 0-sized file existed on any of the
> master_sites. If you can reproduce that problem, please send the debug
> output.

Ok I'll try, it happened when I updated the file on the n.ethz.ch server
(with a different name). I used the debug output to get the new hash.
Somehow I got the hash value for a 0 sized file, which I only noticed
later when I discovered that the installation was incomplete.

Anyway I'll try it again.