Update PVector functions

Test Plan:
- Run code from http://pastebin.com/F1eQV97n
Update PVector functions

Test Plan: - Run code from http://pastebin.com/F1eQV97n

Reviewers: john

Differential Revision: http://phabricator.khanacademy.org/D6547
Merge branch 'pf-update-pvector' of https://github.com/Khan/processing-js into pf-update-pvector
Merge pull request #1 from Khan/pf-update-pvector

Update PVector