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