Normalize dir path in AutoLoaderStructureTest

Normalize dir path in AutoLoaderStructureTest

The file paths we inspect are always normalized (File_Iterator_Facade
applies realpath()), but the directory we compare against may not be,
depending on how wfLoadExtension() was called. Normalize the directory
before we remove the directory prefix from each file, so that we don’t
end up stripping away the wrong parts of the path.

Change-Id: Ib272fb892c18d989f8d439ed50c6a5a8fd542cc9