Windows: Make OpenSSH properly detect tty detachment.

Windows: Make OpenSSH properly detect tty detachment.

Apparently, CREATE_NO_WINDOW makes the OS tell the process
that it has a console, but without actually creating the
window. As a result, when git is started from GUI, ssh
tries to ask its questions on the invisible console.

This patch uses DETACHED_PROCESS instead, which clearly
means that the process should be left without a console.
The downside is that if the process manually calls
AllocConsole, the window will appear. A similar thing
might occur if it calls another console executable.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Acked-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>