update fairseq binarizer to use PathManager
update fairseq binarizer to use PathManager

Summary:
Currently, fairseq binarizer does not work with Manifold files, making it incompatible with some internal procedures. This change preserves the old functionality while allowing Manifold files to be passed into binarizer functions.

motivated by theweiho: "I think we should change Binarizer to use PathManager so that it can handle either Manifold path or POSIX path" (D22241626)

Reviewed By: akinh

Differential Revision: D22293525

fbshipit-source-id: d1bf4f8b50dda6a9214ee2fbe45e112ca9628f60

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq