Fixed OSError "No such file or directory: None" and make IOError consistent. The None error occurs when the current working directory is no longer available, e.g. because it was removed in another shell.

#!/bin/sh

mkdir a
cd a
hg init
echo foo > b
hg add b
hg ci -m "b" -d "1000000 0"

chmod -w .hg

cd ..

hg clone a b

chmod +w a/.hg # let test clean up

cd b
hg verify