Implemented __dirname

It seems that the current __filename module global is mainly used to
determine the directory the current module is in. To make that
easier, this patch adds support for a __dirname module global
directly.

doc/api.txt

@@ -64,6 +64,9 @@ The search path for absolute path arguments to +require()+.
 +__filename+ ::
 The filename of the script being executed.
 
++__dirname+ ::
+The dirname of the script being executed.
+
 +module+ ::
 A reference to the current module (of type +process.Module+). In particular
 +module.exports+ is the same as the +exports+ object. See +src/process.js+ for

src/node.js

@@ -919,13 +919,13 @@ Module.prototype.loadScript = function (filename, loadPromise) {
     require.async = requireAsync;
     require.main = process.mainModule;
     // create wrapper function
-    var wrapper = "var __wrap__ = function (exports, require, module, __filename) { "
+    var wrapper = "var __wrap__ = function (exports, require, module, __filename, __dirname) { "
                 + content
                 + "\n}; __wrap__;";
 
     try {
       var compiledWrapper = process.compile(wrapper, filename);
-      compiledWrapper.apply(self.exports, [self.exports, require, self, filename]);
+      compiledWrapper.apply(self.exports, [self.exports, require, self, filename, path.dirname(filename)]);
     } catch (e) {
       loadPromise.emitError(e);
       return;

test/mjsunit/test-module-loading.js

@@ -6,7 +6,7 @@ var a = require("./fixtures/a");
 var d = require("./fixtures/b/d");
 var d2 = require("./fixtures/b/d");
 // Absolute
-var d3 = require(require('path').dirname(__filename)+"/fixtures/b/d");
+var d3 = require(__dirname+"/fixtures/b/d");
 // Relative
 var d4 = require("../mjsunit/fixtures/b/d");
 
@@ -52,6 +52,8 @@ try {
   assert.equal("blah", e.message);
 }
 
+assert.equal(require('path').dirname(__filename), __dirname);
+
 process.addListener("exit", function () {
   assert.equal(true, a.A instanceof Function);
   assert.equal("A done", a.A());