fix AsyncCreatable options parsing

fixes JedWatson#1279

src/AsyncCreatable.js

@@ -1,6 +1,15 @@
 import React from 'react';
 import Select from './Select';
 
+function reduce(obj, props = {}){
+  return Object.keys(obj)
+  .reduce((props, key) => {
+    const value = obj[key];
+    if (value !== undefined) props[key] = value;
+    return props;
+  }, props);
+}
+
 const AsyncCreatable = React.createClass({
 	displayName: 'AsyncCreatableSelect',
 
@@ -11,12 +20,15 @@ const AsyncCreatable = React.createClass({
 					<Select.Creatable {...this.props}>
 						{(creatableProps) => (
 							<Select
-								{...asyncProps}
-								{...creatableProps}
+								{...reduce(asyncProps, reduce(creatableProps, {}))}
 								onInputChange={(input) => {
 									creatableProps.onInputChange(input);
 									return asyncProps.onInputChange(input);
 								}}
+								ref={(ref) => {
+									creatableProps.ref(ref);
+									asyncProps.ref(ref);
+								}}
 							/>
 						)}
 					</Select.Creatable>