Quote some object literal keys in minified version of React.

The original React source has a few object literals where it expects the key
names to not get renamed. The source has the property names quoted, which
has the correct effect of indicating to the Closure Compiler to not do renaming
(see for example https://github.com/facebook/react/blob/0de20e35bc3a9a2356b047fa7fd2d2f79067b8d5/src/browser/ui/ReactDOMComponent.js#L41).
However, the minified versions of React do not have these quotes, presumably
because the minifier decided that they were unncessary.

It's perhaps a bad idea to use the minified version of React as an input to the
Closure Compiler, but since it has other desirable properties (smaller code size
since all runtime warnings and propType checking is disabled), adding the quotes
back is necessary to avoid bugs due to property name lookups failing
mysteriously.

demo/plovr-config.js

@@ -2,7 +2,7 @@
   "id": "demo",
   "paths": ".",
   "inputs": [
-    "react-0.13.1-build/react-with-addons.js",
+    "react-0.13.1-build/react.js",
     "index.js"
   ],
   "mode": "ADVANCED",