[exim] workaround for incoming CR NUL dot CR LF bug

We're having a problem with an Exchange 5.5 server sending to
an Exim 4.41 server. It would appear that the Exchange server
occasionally tries to terminate a message by sending CR(hex 0D)
NUL(00) .(2E) CR(0D) LF(0A). The Exim spec says that CR . CR
is not recognized as a message terminator, and I guess this is
basically the same thing; what we see is that Exim never
responds with a 250, and eventually the whole thing times
out.

Now, the right thing would probably be to fix or upgrade the
Exchange server, but in the meantime, I thought I would
check to see if anyone had ever encountered anything like
this before, and what, if any, workarounds might be available?

- Dale