Windows port: add option for control of IP address changes notification in squid...

Windows port: add option for control of IP address changes notification in squid.conf

On Windows Squid by default will monitor IP address changes and will
reconfigure itself after any detected event. This is very useful for
proxies connected to internet with dial-up interfaces.
In some cases (a Proxy server acting as VPN gateway is one) it could be
desiderable to disable this behaviour.

Also fixed build error on Cygwin