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>

diff -dur duma_2_5_1.orig/Makefile duma_2_5_1/Makefile

--- duma_2_5_1.orig/Makefile	2007-07-11 17:49:43.000000000 +0200

+++ duma_2_5_1/Makefile	2007-07-11 17:50:46.000000000 +0200

@@ -115,9 +115,14 @@

 	dumatest.c tstheap.c dumatestpp.cpp testoperators.cpp \

 	createconf.c

-OBJECTS = dumapp.o duma.o sem_inc.o print.o

+OBJECTS = duma.o sem_inc.o print.o

+SO_OBJECTS = duma_so.o sem_inc_so.o print_so.o

+

+ifeq ($(DUMA_CPP),1)

+OBJECTS += dumapp.o

+SO_OBJECTS += dumapp_so.o

+endif

-SO_OBJECTS = dumapp_so.o duma_so.o sem_inc_so.o print_so.o

 all:	libduma.a $(DUMASO) tstheap dumatest dumatestpp testoperators tstheap_so dumatestpp_so

 	@ echo "Testing DUMA."