Update civetweb.c
Update civetweb.c

Updated to build clean in Visual Studio 2012 & 64 bit.
The undef of _WIN32_WINNT is out dated at this point.

ws2tcpip.h needed to be defined in windows.

HAVE_POLL is defined in this new include, so we don't want to define it again.

GerHobbelt/civet-webserver,GerHobbelt/civet-webserver,GerHobbelt/civet-webserver,GerHobbelt/civet-webserver,GerHobbelt/civet-webserver,GerHobbelt/civet-webserver