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 a > a
hg add a
hg commit -m "test" -d "0 0"
hg history
hg tag -d "0 0" "bleah"
hg history

echo foo >> .hgtags
hg tag -d "0 0" "bleah2" || echo "failed"