Detect invalid HTTP storage server responses early, close request

[itamarst]

When downloading shares, if the Content-Length/Content?-Range of a response doesn't match requested body length (too short means we were wrong about what server has in terms of length, or server bug, too long means server bug), we should probably just give up early.

This depends on #3907; currently we knowingly send non-matching lengths, so that needs to be fixed first.

It also depends on ​https://github.com/twisted/treq/issues/347 to make this possible at all.

Implementation: when deliverBody() happens the passed-in protocol gets access to the transport, allowing us to close the connection.