Fixing #1774 about issues when running node with --harmony_block_scoping v8 option

Fixes #1837.

lib/fs.js

@@ -412,7 +412,7 @@ fs.readlinkSync = function(path) {
 fs.symlink = function(destination, path, mode_, callback) {
   var mode = (typeof(mode_) == 'string' ? mode_ : null);
   var callback_ = arguments[arguments.length - 1];
-  var callback = (typeof(callback_) == 'function' ? callback_ : null);
+  callback = (typeof(callback_) == 'function' ? callback_ : null);
   binding.symlink(destination, path, mode, callback);
 };
 
@@ -564,7 +564,7 @@ function writeAll(fd, buffer, offset, length, callback) {
 fs.writeFile = function(path, data, encoding_, callback) {
   var encoding = (typeof(encoding_) == 'string' ? encoding_ : 'utf8');
   var callback_ = arguments[arguments.length - 1];
-  var callback = (typeof(callback_) == 'function' ? callback_ : null);
+  callback = (typeof(callback_) == 'function' ? callback_ : null);
   fs.open(path, 'w', 0666, function(openErr, fd) {
     if (openErr) {
       if (callback) callback(openErr);
@@ -747,7 +747,7 @@ if (isWindows) {
 
   // windows version
   fs.realpathSync = function realpathSync(p, cache) {
-    var p = path.resolve(p);
+    p = path.resolve(p);
     if (cache && Object.prototype.hasOwnProperty.call(cache, p)) {
       return cache[p];
     }
@@ -762,7 +762,7 @@ if (isWindows) {
       cb = cache;
       cache = null;
     }
-    var p = path.resolve(p);
+    p = path.resolve(p);
     if (cache && Object.prototype.hasOwnProperty.call(cache, p)) {
       return cb(null, cache[p]);
     }