child_process: make copy of options arg

Make a copy of the options object that the user passes in, we modify it.

lib/child_process.js

@@ -172,10 +172,10 @@ exports.fork = function(modulePath /*, args, options*/) {
   var options, args, execArgv;
   if (Array.isArray(arguments[1])) {
     args = arguments[1];
-    options = arguments[2] || {};
+    options = util._extend({}, arguments[2]);
   } else {
     args = [];
-    options = arguments[1] || {};
+    options = util._extend({}, arguments[1]);
   }
 
   // Prepare arguments for fork:
@@ -264,15 +264,12 @@ exports.execFile = function(file /* args, options, callback */) {
 
   if (Array.isArray(arguments[1])) {
     args = arguments[1];
-    if (typeof arguments[2] === 'object') optionArg = arguments[2];
+    options = util._extend(options, arguments[2]);
   } else {
     args = [];
-    if (typeof arguments[1] === 'object') optionArg = arguments[1];
+    options = util._extend(options, arguments[1]);
   }
 
-  // Merge optionArg into options
-  util._extend(options, optionArg);
-
   var child = spawn(file, args, {
     cwd: options.cwd,
     env: options.env,