Visual Studio 2012 RC

The attached patch makes postgres build with Visual Studio 2012 RC.

As MS finally decided on the name I don't expect any need for changes
for the final RTM.

I didn't bother to update the docs for now as I still have some hope
that the developer community succeds in pushig M$ to reverse this decision:

http://people.planetpostgresql.org/andrew/index.php?/archives/276-Microsoft-throws-large-developer-communities-under-the-bus.html

Regards,
Brar