[2036] Return non-zero exit status when valgrind finds an issue

This should work fine with make check, so long as we have all issues
fixed or covered by suppressions. In this case, whenever a new issue
is introduced, make check would fail.

configure.ac

@@ -991,7 +991,7 @@ AC_ARG_ENABLE(valgrind, [AC_HELP_STRING([--enable-valgrind],
 AM_CONDITIONAL(ENABLE_VALGRIND, test "x$enable_valgrind" != "xno")
 
 if test "x$VALGRIND" != "xno" -a "x$enable_valgrind" != "xno"; then
-   VALGRIND_COMMAND="$VALGRIND -q --gen-suppressions=all --suppressions=\$(top_srcdir)/src/valgrind-suppressions --suppressions=\$(top_srcdir)/src/valgrind-suppressions.revisit --num-callers=24 --leak-check=full --fullpath-after="
+   VALGRIND_COMMAND="$VALGRIND -q --error-exitcode=1 --gen-suppressions=all --suppressions=\$(top_srcdir)/src/valgrind-suppressions --suppressions=\$(top_srcdir)/src/valgrind-suppressions.revisit --num-callers=24 --leak-check=full --fullpath-after="
 fi
 AC_SUBST(VALGRIND_COMMAND)