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.
merge: warning: conflicts during mergemerging amerging a failed!32e80765d7fe+75234512624c+ tipsomething else=======somethingM a