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/runtime.js

@@ -0,0 +1,15 @@
+require('./common');
+
+global.Handlebars = require('../../dist/handlebars.runtime');
+
+var compiler = require('../../lib/handlebars');
+
+global.CompilerContext = {
+  compile: function(template, options) {
+    var templateSpec = compiler.precompile(template, options);
+    return Handlebars.template(eval('(' + templateSpec + ')'));
+  },
+  compileWithPartial: function(template, options) {
+    return compiler.compile(template, options);
+  }
+};