Add support for PDF.js 1.0.712

This updates the PDF.js glue code to work with PDF.js 1.0.712, which is shipped in FF32. (Currently in beta.)

Merge https://github.com/hypothesis/annotator/pull/76 first; the only new change on this branch is https://github.com/hypothesis/annotator/commit/0bc62e043274ad4f45b5b343d755f923018f5966.