* src/xend_internal.c, src/xm_internal.c: pass the
        connection to virDomainParseXMLDesc()

        * src/xml.[ch]: make virDomainParseXMLDesc accept
        a virConnectPtr so that we can use it later to
        lookup the bridge associated with a network

        * tests/xml2sexprtest.c: just pass NULL here, it's
        safe