Allow calling fork() without args or options

Closes GH-2424

doc/api/child_processes.markdown

@@ -198,7 +198,7 @@ subshell but rather the specified file directly. This makes it slightly
 leaner than `child_process.exec`. It has the same options.
 
 
-### child_process.fork(modulePath, arguments, options)
+### child_process.fork(modulePath, [arguments], [options])
 
 This is a special case of the `spawn()` functionality for spawning Node
 processes. In addition to having all the methods in a normal ChildProcess

lib/child_process.js

@@ -160,13 +160,23 @@ function setupChannel(target, channel) {
 
 function nop() { }
 
+exports.fork = function(modulePath /*, args, options*/) {
 
-exports.fork = function(modulePath, args, options) {
-  if (!options) options = {};
+  // Get options and args arguments.
+  var options, args;
+  if (Array.isArray(arguments[1])) {
+    args = arguments[1];
+    options = arguments[2] || {};
+  } else {
+    args = [];
+    options = arguments[1] || {};
+  }
 
-  args = args ? args.slice(0) : [];
+  // Copy args and add modulePath
+  args = args.slice(0);
   args.unshift(modulePath);
 
+  // Don't allow stdinStream and customFds since a stdin channel will be used
   if (options.stdinStream) {
     throw new Error('stdinStream not allowed for fork()');
   }