This fixes a longstanding glibc bug concerning backreferences
<https://sourceware.org/11053> (2009-12-04).
* lib/regexec.c (proceed_next_node, push_fail_stack)
(pop_fail_stack): Push and pop the previous registers
as well as the current ones. All callers changed.
(set_regs): Also pop if CUR_NODE has already been checked,
so that it does not get added as a duplicate set entry.
(update_regs): Fix comment location.
* tests/test-regex.c (tests): New constant.
(bug_regex11): New test function.
(main): Bump alarm value. Call new test function.