Fix tgz archival on Windows. Making tgz's on Windows has been broken by 06de65673ec2 due to not being careful enough about binary mode opens.

#!/bin/sh

mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m test -d "1000000 0"
hg history
hg manifest --debug
hg cat a
hg verify