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 123 > a
hg add a
hg commit -m "a" -u a -d "0 0"
cd ..
mkdir b
cd b
hg init
echo 321 > b
hg add b
hg commit -m "b" -u b -d "0 0"
hg pull ../a
hg heads