[zeromq-dev] a little patch for clock.cpp

[Martin Sustrik]

Hi Oleg,
> I try to build last git in MSVC 2005 but compiler not found __rdtsc () 
> fucntion. I make changes in clock.cpp and send patch file.
b
Two issues:

1. I believe _MSC_VER should be used instead of ZMQ_HAVE_WINDOWS to keep 
the MinGW build OK. (Not sure about Cygwin though...)

2. Please, do sign-off the patch. See here: 
http://www.zeromq.org/docs:contributing#toc6

Thanks!
Martin