add a torture target

Original commit message from CVS:
add a torture target
diff --git a/Makefile.am b/Makefile.am
index 06fdfc3..9c4c93b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -44,3 +44,6 @@
 
 check-valgrind:
 	cd check && make check-valgrind
+
+check-torture:
+	cd check && make check-torture