React has a dev and prod version. The dev version includes additional
sanity checks and better errors, but at a slight perf cost. The prod
version available on the web is by default minified, but we don't want
a minified version, so we need to build it ourselves.

In bug 1217979, we are only using react in development environment for now until
we can think of a way to conditionally build these different versions, so
the `react.js` here is the dev environment one and generated with the following steps:

* git clone https://github.com/facebook/react.git && cd react
* npm install
* grunt build
* cp build/react-with-addons.js <gecko-dev>/devtools/client/shared/vendor/react.js

For production, which we do not currently have:
* NODE_ENV=production grunt build
* cp build/react-with-addons.js <gecko-dev>/devtools/client/shared/vendor/react.js

The second build produces a non-minified React file but with all the
sanity checks that incur a perf hit removed.

You also need to copy the ReactDOM package. It requires React, so
right now we are just manually changing the path from `react` to
`devtools/client/shared/vendor/react`.

* cp build/react-dom.js <gecko-dev>/devtools/client/shared/vendor/react-dom.js
* (change `require('react')` at the top of the file to the right path)
