fix #3275 with solution from https://gnunet.org/bugs/view.php?id=3275#c8029

sed -i 's#^\(\s*\)TESTS#\1TESTS_ENVIRONMENT=export GNUNET_PREFIX=@prefix@;export PATH=@prefix@/bin:$$PATH;\n&#'



git-svn-id: https://gnunet.org/svn/gnunet@32027 140774ce-b5e7-0310-ab8b-a85725594a96