Remove process.mixin dependency from fs

lib/fs.js

@@ -444,7 +444,8 @@ var FileReadStream = exports.FileReadStream = function(path, options) {
   this.mode = 0666;
   this.bufferSize = 4 * 1024;
 
-  process.mixin(this, options || {});
+  options = options || {};
+  for (var i in options) this[i] = options[i];
 
   var
     self = this,
@@ -555,7 +556,8 @@ var FileWriteStream = exports.FileWriteStream = function(path, options) {
   this.encoding = 'binary';
   this.mode = 0666;
 
-  process.mixin(this, options || {});
+  options = options || {};
+  for (var i in options) this[i] = options[i];
 
   var
     self = this,