Major Twisted Words update

From the commit message:

This is a complete rewrite of the twisted.words server code. Botbot and Tendril features are dropped for the time being. Provided is a generic chat server accessible via IRC and PB, and with a plugin mechanism for adding new protocols. Authentication is done via newcred; unlike the previous revision, there is no support for registering new users through the server. This should be dealt with using a generic checker manipulation system (so that any checker configuration can be manipulated, rather than one or two I choose to support in words).

Webwords is also gone, as there are no exciting web technologies in Twisted. The plugin mechanism is, however, used to provide a Nevow LivePage interface to the chat service which could be extended to perform all the same tasks previously covered by Webwords.

t-im may or may not still work.

How Not To Make A Page-Atomic Copy Of A File

Can you find the hidden bug?

import os

def copy(fIn, fOut):
    blockSize = os.statvfs(fIn.name).f_bsize
    while 1:
        bytes = fIn.read(blockSize)
        if not bytes:
            break
        fOut.write(bytes)