These lines were introduced here: https://github.com/nltk/nltk/commit/1ecbd2edc32db24b4e6c7dd8555d0b89c668f041
It seems they fix an issue with .svn folders. We use git now,
there are no .svn folders.

See also: http://stackoverflow.com/questions/1129180/how-can-i-make-setuptools-ignore-subversion-inventory