Fixed issue where Launcher's spawning of Pageant wasn't properly
detaching from launcher.exe.  (It's necessary to tell subprocess
that you don't want launcher.exe to connect to the stdin, stdout,
and stderr streams of the child process, otherwise when you install
a new version of the Launcher, you will get an error saying that
launcher.exe can't be overwritten because it is in use (because
it is connected to the stdout stream of its child Pageant process.)