extensions: catch OSError when hgext is not accessible (issue1708) Temporary workaround for issue1708: on win32 with py2exe, hgext is distributed inside a zipped file (which anyway does not contain the py files from which we ought to extract the documentation strings), which raises a WindowsError (subclasses OSError). This means that on such platforms the list of disabled extensions won't be available. Real fix postponed for after Mercurial 1.3.