Fix walkhelper on windows.
The ''seen'' dictionary stores paths in canonical form,
so the walkhelp must also provide paths in that form,
otherwise the changed files are listed twice.
#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "0 0"
ls
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "0 0"
hg co 0
# B should disappear
ls