[refactor api] Start using native fork

Get rid of `node-fork`.

So far this only works on `node v0.7.x` due to usage of `silent` option
in `child_process.fork` options.

This also adds a `fork-shim`, which allows us to spawn arbitrary
commands using `child_process.fork`.

bin/fork-shim

@@ -0,0 +1,5 @@
+#!/usr/bin/env node
+var spawn = require('child_process').spawn;
+spawn(process.argv[2], process.argv.slice(3), {
+  customFds: [0, 1, 2]
+});

lib/forever/monitor.js

@@ -9,9 +9,9 @@
 var events = require('events'),
     fs = require('fs'),
     path = require('path'),
-    nodeFork = require('node-fork'),
-    fork = nodeFork.fork,
-    spawn = require('child_process').spawn,
+    child_process = require('child_process'),
+    fork = child_process.fork,
+    spawn = child_process.spawn,
     broadway = require('broadway'),
     psTree = require('ps-tree'),
     winston = require('winston'),
@@ -75,7 +75,6 @@ var Monitor = exports.Monitor = function (script, options) {
   this.spawnWith = options.spawnWith || {};
   this.sourceDir = options.sourceDir;
   this.fork      = options.fork || false;
-  this.forkShim  = options.forkShim || false;
   this.cwd       = options.cwd || null;
   this.hideEnv   = options.hideEnv || [];
   this._env      = options.env || {};
@@ -216,17 +215,10 @@ Monitor.prototype.trySpawn = function () {
 
   if (this.fork) {
     this.spawnWith.silent = true;
-    this.spawnWith.command = this.command;
-
-    if (this.forkShim) {
-      if (typeof this.forkShim === 'string') {
-        this.spawnWith.forkModule = this.forkShim;
-      }
-      this.spawnWith.env['FORK_SHIM'] = true;
-      return nodeFork.shim.fork(this.args[0], this.args.slice(1), this.spawnWith);
-    }
-
-    return fork(this.args[0], this.args.slice(1), this.spawnWith);
+    return fork(
+      path.join(__dirname, '..', '..', 'bin', 'fork-shim'),
+      [this.command].concat(this.args), this.spawnWith
+    );
   }
 
   return spawn(this.command, this.args, this.spawnWith);