The second argument to the typeName function should be the ID of
a type, not a value. As typeName does no checking on it's arguments
it'll form a negative index for accessing the type names array.

Patch by Emden R. Gansner <erg@research.att.com> 

Index: lib/gvpr/compile.c
===================================================================
--- lib/gvpr/compile.c.orig	2009-11-22 20:10:33.000000000 +0100
+++ lib/gvpr/compile.c	2010-06-01 12:52:04.902610547 +0200
@@ -1514,7 +1514,7 @@ setval(Expr_t * pgm, Exnode_t * x, Exid_
 		state->tvt = (trav_type) iv;
 	    else
 		error(1, "unexpected value %d assigned to %s : ignored",
-		      iv, typeName(pgm, V_travtype));
+		      iv, typeName(pgm, T_tvtyp));
 	    break;
 	case V_travroot:
 	    np = INT2PTR(Agnode_t *, v.integer);