ECB - edit for new exchange rate provider

[beetea]

The ECB exchange rate module does not handle every currency, so I modified it for another XML feed found here: http://www.floatrates.com/daily/usd.xml

I've modified the ECB code like so:

Line 24:

const SERVICE_URL = 'http://www.floatrates.com/daily/usd.xml';

starting line 147:

$this->serviceCache['USD'] = 1.0;
foreach ($XML->xpath('//item') as $entry) {
    $this->serviceCache[(string) $entry->targetCurrency] =
        (float) $entry->exchangeRate;
}

Seems to work. There are other feeds at the same site for other base currencies, in which case you'd have to modify the SERVICE_URL and the base currency ['USD']