Makefile: run 'npm install' whenever 'package.json' is updated.
Makefile: run 'npm install' whenever 'package.json' is updated.

- Make 'node_modules' an order-only dependency of 'bin/dep.mk'
- Add the 'source-map' dependencies to SourceMapIntegration.js

BUG=http://code.google.com/p/traceur-compiler/issues/detail?id=224
TEST=None

Review URL: https://codereview.appspot.com/7681046
Patch from Ben Chan <usrbincc@yahoo.com>.

rossberg-chromium/traceur-soundscript,sebgod/traceur-compiler,rossberg-chromium/traceur-soundscript,ericmckean/traceur-compiler,guybedford/traceur-compiler,bazaarvoice/traceur-compiler,lintangarief/traceur-compiler,astralfoxy/mirai-traceur,pandoraui/traceur-compiler,sebmck/traceur-compiler,sid0818/traceur-compiler,bazaarvoice/traceur-compiler,google/traceur-compiler,kittens/traceur-compiler,vicb/traceur-compiler,johnjbarton/traceur-compiler,mathiasbynens/traceur-compiler,renie/traceur-compiler,kittens/traceur-compiler,longze/traceur-compiler,bjlxj2008/traceur-compiler,longze/traceur-compiler,arv/traceur-compiler,wilsonokibe/traceur-compiler,arv/traceur-compiler,bjlxj2008/traceur-compiler,ericmckean/traceur-compiler,wilsonokibe/traceur-compiler,vicb/traceur-compiler,johnjbarton/traceur-compiler,renie/traceur-compiler,sebmck/traceur-compiler,lintangarief/traceur-compiler,sid0818/traceur-compiler,rwaldron/traceur-compiler,google/traceur-compiler,sebgod/traceur-compiler,pandoraui/traceur-compiler