adding module tests for .js and bare files

Currently the module tests don't cover the cases for when a user
requires a file with a request that includes the extension, and for a
request to a file with no extensions.

ex.

require("./a.js") // not tested
require("./foo") // (not tested with trying to load a file named ./foo)

test/simple/test-module-loading.js

@@ -5,6 +5,14 @@ var path = require('path'),
 
 common.debug("load test-module-loading.js");
 
+// require a file with a request that includes the extension
+var a_js = require("../fixtures/a.js");
+assert.equal(42, a_js.number);
+
+// require a file without any extensions
+var foo_no_ext = require("../fixtures/foo");
+assert.equal("ok", foo_no_ext.foo);
+
 var a = require("../fixtures/a");
 var c = require("../fixtures/b/c");
 var d = require("../fixtures/b/d");