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

hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "0 0"
touch b
hg add b
rm b
hg commit -A -m"comment #1" -d "0 0"