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/ktlpnikvdwgbvfaam...@forum.dlang.org
import core.sys.windows.windows : GetConsoleCP;
bool hasConsole = !!GetConsoleCP();

Thanks.