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/node.js

@@ -0,0 +1,13 @@
+require('./common');
+
+global.Handlebars = require('../../lib/handlebars');
+
+global.CompilerContext = {
+  compile: function(template, options) {
+    var templateSpec = Handlebars.precompile(template, options);
+    return Handlebars.template(eval('(' + templateSpec + ')'));
+  },
+  compileWithPartial: function(template, options) {
+    return Handlebars.compile(template, options);
+  }
+};