(id_gn): Exit 77, not 1, for a test-framework

failure, so that doesn't cause `make check' to stop.  Nelson Beebe
reported that this test would fail with this diagnostic
`cannot find name for group ID 10' on one of his systems.

tests/chown/separator

@@ -30,7 +30,7 @@ test -n "$id_gn" || framework_failure=1
 
 if test $framework_failure = 1; then
   echo "$0: failure in testing framework" 1>&2
-  (exit 1); exit 1
+  (exit 77); exit 77
 fi
 
 fail=0