tests: add some missing "set -e"

* src/ltltest/lbt.test, src/ltltest/utf8.test,
src/tgbatest/dbacomp.test, src/tgbatest/ltlcross.test,
src/tgbatest/ltlcross2.test, src/tgbatest/ltlcrossce.test: Add set -e.

src/ltltest/lbt.test

@@ -19,6 +19,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 . ./defs
+set -e
 
 ltlfilt=../../bin/ltlfilt
 randltl=../../bin/randltl

src/ltltest/utf8.test

@@ -1,5 +1,5 @@
 #! /bin/sh
-# Copyright (C) 2012 Laboratoire de Recherche et Developpement
+# Copyright (C) 2012, 2013 Laboratoire de Recherche et Developpement
 # de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -21,6 +21,7 @@
 # Make sure
 
 . ./defs || exit 1
+set -e
 
 # ----
 run 0 ../ltl2text '□◯a' >out