Input Patch

Fixed Laravel from re-indexing the input array. Only happens if input names are numbers. This was caused by merging the arrays with array_merge when the array union should of been used.

PHP Reference: http://php.net/array_merge (Example 3)
Minimum Code: http://paste.laravel.com/stF

---------------

Fixed a bug introduced with commit 41ec1e0. Input::only would only return the keys that existed. Before it would return with the default value of null.
```php
$input = Input::get('email', 'password');

//If password wasn't submitted then this will throw undefined variable
$password = Hash::make($input['password']);
```