#63 Multiple chunk request

[fabiano]

There are threads about asyncronous vs sync download.
I think that the right solution stay in the middle.
By implementing a new type of file req,not quering for
chunk #1, but query for #1-#30.. with a single query
you can request 30 chuks(less requests-->network
efficiency).
This is ideal for multisource segmented downlaod ..so
you can request a portion of file from one guy and a
portion from another.

The advantages are similar to asyncronous( you can send
more chunks first of receving the new request! that was
done after receving the chunk correctly, this method
had introduced delay and bandwith limit).

After a timeout not received chunks are requested
again(hopefully it is a rare event)