Previous patch did not work on MacOS X, and I don't have shell

access to that host.

* src/tgbatest/kv.test: Use ${DOT-true} instead of ${DOT-:}.  I
don't know, the MacOS shell must be mixing the syntaxes for
${DOT:-} and ${DOT-:}.
* iface/nips/nipstest/dotty.test: Likewise

src/tgbatest/kv.test

@@ -27,7 +27,7 @@ set -e
 check ()
 {
   run 0 ../ltl2tgba -f -KV "$1" > out.dot
-  "${DOT-:}" out.dot > /dev/null
+  "${DOT-true}" out.dot > /dev/null
   rm -f out.dot
 }