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.
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%% uncompressed contents in repo
this is a test
%% uncompress our working dir copy
this is a test
%% uncompress our new working dir copy
this is a test