Add configuration for running tests with Jest

Can be run with `node_modules/.bin/jest` for now; didn't want to disturb the grunt setup.

Right now one test fails with:

```
 FAIL  browser/ui/__tests__/ReactDOMComponent-test.js (1.423s)
● ReactDOMComponent › updateDOM › it should update styles when mutating style object
  - Expected: '0' toEqual: '0.5'
        at Spec.<anonymous> (src/browser/ui/__tests__/ReactDOMComponent-test.js:99:33)
```

which I can only assume is a jsdom problem -- no other asserts fail.

jest/environment.js

@@ -0,0 +1 @@
+__DEV__ = true;

jest/preprocessor.js

@@ -0,0 +1,9 @@
+"use strict";
+
+var ReactTools = require('../main.js');
+
+module.exports = {
+  process: function(src) {
+    return ReactTools.transform(src, {harmony: true});
+  }
+};

package.json

@@ -54,6 +54,7 @@
     "grunt-contrib-jshint": "~0.8.0",
     "gzip-js": "~0.3.2",
     "jasmine-tapreporter": "~0.2.2",
+    "jest-cli": "~0.1.5",
     "lodash": "~2.4.1",
     "microtime": "~0.5.1",
     "optimist": "~0.6.0",
@@ -77,5 +78,13 @@
   },
   "scripts": {
     "test": "./node_modules/.bin/grunt test"
+  },
+  "jest": {
+    "rootDir": "src",
+    "scriptPreprocessor": "../jest/preprocessor.js",
+    "setupEnvScriptFile": "../jest/environment.js",
+    "unmockedModulePathPatterns": [
+      ""
+    ]
   }
 }