multipart and multi-proxy transfer support

[anonymous]

1. using multipart transfer, we can divide one file into

several part, transfer each part individualy and
simultaneously, then merge then into one file.

2. using multi-proxy transfer, we can transfer several

files or several part of one file at the same time with a
server that has session limited per IP. For example, we
have a server X allow only 1 session for one IP, and we
have 4 proxy a, b, c, d. We can transfer file1 from X
directly, and transfer file2 simultaneously through a,
transfer file3 through b, and so on. Or transfer part1 of a
file from X directly, part2 of that file through a, and so on.
This can break the session limition of the server,
especially with speed limition per session. Of course,
some strategy may be included, e.g. how many session
per IP is allowed for the server, which proxy can be
used as one of multi-proxy, distribute one transfer task
to as many proxy as possible first or to one proxy as
possible as server support first.