Get back a SOAP message.

def ReceiveSOAP(self, readerclass=None, **kw):
        '''Get back a SOAP message.
        '''
        if self.ps: return self.ps
        if not self.IsSOAP():
            raise TypeError(
                'Response is "%s", not "text/xml"' % self.reply_headers.type)
        if len(self.data) == 0:
            raise TypeError('Received empty response')

        self.ps = ParsedSoap(self.data, 
                        readerclass=readerclass or self.readerclass, 
                        encodingStyle=kw.get('encodingStyle'))

        if self.sig_handler is not None:
            self.sig_handler.verify(self.ps)

        return self.ps