scripts: add option to start an interactive debug shell

Add an option that, when a command fails:
- starts an interactive shell with the failed command's environment
- attempts re-execution of the failed command, continues, or aborts
at user's whim.

Before starting the debug-shell, the backtrace is printed.
When exiting for an abort, the standard error message is printed.

Based on an idea and a patch from: Johannes Stezenbach <js@sig21.net>
http://sourceware.org/ml/crossgcc/2012-09/msg00144.html

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[yann.morin.1998@free.fr: integrate in the fault handler]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Johannes Stezenbach <js@sig21.net>
Patchwork-Id: 191571
Patchwork-Id: 191668

syntax: glob

# Generated files

configure

autom4te.cache

config.log

config.status

Makefile

*ct-ng*

docs/*ct-ng*.1

docs/*ct-ng*.1.gz

paths.mk

paths.sh

scripts/crosstool-NG.sh

scripts/saveSample.sh

scripts/showTuple.sh

kconfig/conf

kconfig/?conf

kconfig/**.o

kconfig/**.dep

kconfig/lex.backup

kconfig/lex.zconf.c

kconfig/zconf.hash.c

kconfig/zconf.tab.c

config/configure.in

config.gen/

.config

.config.2

# Temporaries

.*.swp

build.log

.config.old

# This is the place where toolchains are built

.build/

# .. and the legacy location

targets/