Added trace option

The methods __getLastRequest, __getLastRequestHeaders, __getLastResponse and __getLastResponseHeaders only work if the SoapClient object was created with the trace option set to TRUE.
Usage:
SoapWrapper::add(function ($service) {
    $service->name('currency')->trace(TRUE)->wsdl('http://currencyconverter.kowabunga.net/converter.asmx?WSDL');
});