Iperf

Hi,
this is a patch that allows to compile iperf under windows xp in visual studio 2003.
It it not heavily tested and might break the compile under unix. But it might be a good starting point to get cross platfrom support back into iperf.
To complete the port I copied a few lines from http://doxygen.postgresql.org/signal_8c-source.html which has as copyright notice
Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group so one would have to check if that is ok and compatible with the iperf license.

Thanks a lot, Fabian