exception due to whitespace in text of tags

[maiermic]

For example, whitespace in relatedStateVariable tag

<argument xmlns="urn:schemas-upnp-org:service-1-0">
		    <name>pairingDeviceID</name>
                    <direction>in</direction>
                    <relatedStateVariable>
                       A_ARG_TYPE_pairingDeviceID
                    </relatedStateVariable>
		</argument>

causes KeyError when its text is used as key (see upnpclient/upnp.py#L300)

arg_statevar = self.statevars[findtext('relatedStateVariable')]

since it contains whitespace. Similar issues occur if text of other tags is used with whitespace.