Nltk: paths in compat.py

[stevenbird]

Use os.path.join() to concatenate paths, in compat.py, cf https://github.com/nltk/nltk/pull/777

[Dobatymo]

was fixed here https://github.com/nltk/nltk/pull/1226 wasn't it?

[alvations]

Yes, it resolved in #1226. Thanks for catching this!

And also thank you for spotting the other lingering issues on the tracker that should have been resolved =)

[stevenbird]

Yes, thanks @Dobatymo