Refactor qunit unit tests

Allows for testing node, browser, and precompiled modes in the node
tests. Also reorganizes the qunit spec file to provide better
organization.

spec/env/runner.js

@@ -0,0 +1,40 @@
+var fs = require('fs'),
+    Mocha = require('mocha'),
+    path = require('path');
+
+var errors = 0,
+    testDir = path.dirname(__dirname),
+    grep = process.argv[2];
+
+var files = fs.readdirSync(testDir)
+      .filter(function(name) { return (/.*\.js$/).test(name); })
+      .map(function(name) { return testDir + '/' + name; });
+
+run('./node', function() {
+  run('./browser', function() {
+    run('./runtime', function() {
+      process.exit(errors);
+    });
+  });
+});
+
+
+function run(env, callback) {
+  var mocha = new Mocha();
+  mocha.ui('bdd');
+  mocha.files = files.slice();
+  if (grep) {
+    mocha.grep(grep);
+  }
+
+  files.forEach(function(name) {
+    delete require.cache[name];
+  });
+
+  console.log('Running env: ' + env);
+  require(env);
+  mocha.run(function(errorCount) {
+    errors += errorCount;
+    callback();
+  });
+}