* src/libvirt.c, src/qemu_internal.c, src/test.c,
	  src/xen_unified.c, src/xend_internal.c,
	  src/libvirt.c, include/libvirt/virterror.h:
	  VIR_ERR_NO_SUPPORT means the function is not supported by
	  the hypervisor.  VIR_ERR_NO_CONNECT means the connection
	  failed.  VIR_ERR_CALL_FAILED is deprecated.  Drivers which
	  decline a URI now no longer produce an error.  Make
	  xen_unified.c ignore naked URI strings like "foo".