fix handling of files of unsupported type in the walk code if a file was of unsupported type, it was considered as 'seen' while walking. this way it was possible to have file in the dirstate not yielded by the walk function.

#!/bin/sh

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

chmod -w .hg

cd ..

hg clone a b
cd b
hg verify

cd ..

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