Description:
------------
Feature Request for the intl extension

The MessageFormatter is capable of formatting a number in a currency 
format. This is only marginally useful because it always uses the 
currency symbol for the locale given to it. 

It probably wouldn't be uncommon to want to display a currency in your 
own currency format, but using a different currency symbol.

Reproduce code:
---------------
<?php

$msgfmt = MessageFormatter::create('nl_NL', 'Price (USD): {0,number,currency}');


/* I'm assuming the format {0,number,currency} is not editable to something like {0,number,currency,USD} because it is defined in a underlying library. So I propose the following new method: */

$msgfmt->setCurrency('USD');

echo $msgfmt->format(array(15.95));

?>



Expected result:
----------------
Price (USD): $ 15,00





Actual result:
--------------
(without the imagined setCurrency call)

Price (USD): ? 15,00