fixed issue #5 using mirc style transfer of files larger 4GB

[seidlmat]

i know this fix seems to be strange on the first look, but it is in fact everything needed regarding the protocoll. A client simply needs to know the amount of data received by the client to know when he can terminate the session.

[pushrax]

From http://www.mirc.com/versions.txt:

20.Added support for the transfer of files larger than four gigabytes.
   This required the following extension to the DCC transfer protocol:
   If mIRC sees that it is sending or receiving a file with a size
   larger than a 32bit value, it sends and expects to receive 64bit
   acks. In all other respects, the protocol is unchanged. Note that
   all previous versions of mIRC are unable to either send or receive
   such large files.

[ProgramComputer]

#10 File length used