use istanbul for code coverage

* Requires no instrumentation
* add `make test-cov` to generate coverage reports
require 'emitter' versus 'emitter-component'

Use the github style dependency to just grab the emitter package from
github. Use the long form because short form is all sorts of broken with
npm.
Merge pull request #131 from shtylman/emitter

require 'emitter' versus 'emitter-component'
Merge pull request #130 from shtylman/coverage

use istanbul for code coverage
Merge branch 'master' of git://github.com/LearnBoost/engine.io-client

Conflicts:
	lib/emitter.js
	package.json