Why double not? (!!)

[Ryan via Digitalmars-d-learn]

Why do I see double `not` operators sometimes in D code? An 
example it the last post of this thread.

http://forum.dlang.org/thread/ktlpnikvdwgbvfaamrsk@forum.dlang.org

> import core.sys.windows.windows : GetConsoleCP;
> bool hasConsole = !!GetConsoleCP();

Thanks.