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

[usrbincc, 2013-03-25 18:29:25]

NOTE: this shell code deletes the local 'node_modules' Not that anyone
has any business putting non-reinstallable stuff in 'node_modules'.

#--cut--
git checkout 2070a8aeb6406db0   # last merge with branch master

dl_check() {
  local f=$(basename $1)
  test -e $f || curl -sO $1
  openssl sha1 < $f | grep -q "= $2" && return 0
  echo sha1 mismatch!
  return 1
}

git checkout -b issue7681046-make-npm-install

dl_check https://codereview.appspot.com/download/issue7681046_1.diff \
  e3473d9729bbdba6 && git apply issue7681046_1.diff

rm -r node_modules
make
touch package.json
make
rm -r node_modules/source-map
make
#--cut--

There are a few other Makefile fixes I have to get to. Mostly
prerequisite fixes and incomplete 'clean' targets.

https://codereview.appspot.com/7681046/diff/1/Makefile
File Makefile (right):

https://codereview.appspot.com/7681046/diff/1/Makefile#newcode74
Makefile:74: node build/expand-js-template.js $< $@
$< indicates the first prerequisite only. Unfortunately, you have to do
something like $(wordlist 1,n,$^) -- untested -- in order to get the
first n prerequisites.

https://codereview.appspot.com/7681046/diff/1/Makefile#newcode77
Makefile:77: node_modules/source-map/lib/source-map/*.js
Eventually I want to generate this, but it's a low priority for now. The
best place to do the fix would be in expand-js-template.js

[arv, 2013-03-25 19:02:00]

LGTM

Committed as 636ed7a8fef2c25e11e72f8b0554afa7da89256f