rx_identity: Add a super user value

Add an RX identity type that can be used to represent the super user
who is granted access using printed tickets.

Change-Id: I3d6e657a04136746b502efa7698901225410f3c0
Reviewed-on: http://gerrit.openafs.org/7261
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>

src/rx/rx_identity.h

@@ -28,6 +28,7 @@
 #include <rx/rx_opaque.h>
 
 typedef enum rx_identity_kind {
+    RX_ID_SUPERUSER = -1,
     RX_ID_KRB4 = 0,
     RX_ID_GSS =  1,
 } rx_identity_kind;