scripts: fix dumping execution backtrace

Dumping the backtrace has been broken since changeset #652e56d6d35a:
scripts: execute each steps in a subshell

We can spawn sub-sub-shells in some cases.

The way the fault handler works is to dump the backtrace, but to avoid
printing it once for every sub-shell (which could get quite confusing),
it simply exits when it detects that it is being run in a sub-shell,
leaving to the top-level shell the work to dump the backtrace.

Because each step is executed in its own sub-shell, the variable arrays
that contain the step name, the source file and line number, are lost
when exiting the per-step sub-shell.

Hence, the backtrace is currently limited to printing only the top-level
main procedure of the shell.

Fix this thus:
- when dumping the bckatraces for the steps & the functions, remember
it was dumped, and only dump it if it was not already dumped
- at the top-level shell, print the hints

Also, rename the top-level step label.

Reported-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 4193d6e6a17430a177fa88c287879c2c35e319f3)

ripped from SuSE

if /etc/resolv.conf is updated, then make sure applications

already running get the updated information.

http://bugs.gentoo.org/177416

diff -durN glibc-2.10.1.orig/resolv/res_libc.c glibc-2.10.1/resolv/res_libc.c

--- glibc-2.10.1.orig/resolv/res_libc.c	2009-02-07 05:27:42.000000000 +0100

+++ glibc-2.10.1/resolv/res_libc.c	2009-11-13 00:49:59.000000000 +0100

@@ -22,6 +22,7 @@

 #include <arpa/nameser.h>

 #include <resolv.h>

 #include <bits/libc-lock.h>

+#include <sys/stat.h>

 /* The following bit is copied from res_data.c (where it is #ifdef'ed

@@ -95,6 +96,20 @@

 __res_maybe_init (res_state resp, int preinit)

 {

 	if (resp->options & RES_INIT) {

+		static time_t last_mtime, last_check;

+		time_t now;

+		struct stat statbuf;

+		

+		time (&now);

+		if (now != last_check) {

+			last_check = now;

+			if (stat (_PATH_RESCONF, &statbuf) == 0 && last_mtime != statbuf.st_mtime) {

+				last_mtime = statbuf.st_mtime;

+				atomicinclock (lock);

+				atomicinc (__res_initstamp);

+				atomicincunlock (lock);

+			}

+		}

 		if (__res_initstamp != resp->_u._ext.initstamp) {

 			if (resp->nscount > 0)

 				__res_iclose (resp, true);