remote-hg: set stdout to binary mode on win32

git clone hangs on windows, and file.write would return errno 22 inside
of mercurial's windows.winstdout wrapper class. This patch sets stdout's
mode to binary, fixing both issues.

[fc: cleaned up]

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>