scripts: fix catching failures

POSIX 1003.1-2008 does not say whether "set -e" should catch a sub-shell
that exits with !0 (it has a list of conditions to catch, but no list of
conditions not to catch, and this situation is not listed).

bash-3 does not catch such a failure, but bash-4 does. That why, on my
Squeeze system I did not see the issue, while Thomas did on is Lenny chroot.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # dmalloc debug facility

 ## depends on ! BACKEND

 ##

 ## help dmalloc helps tracking memory allocation mis-usage

 ## help such as double-free, use-after-free...

 choice

     bool

     prompt "dmalloc version"

 # Don't remove next line

 # CT_INSERT_VERSION_BELOW

 config DMALLOC_V_5_5_2

     bool

     prompt "5.5.2"

 endchoice

 config DMALLOC_VERSION

     string

 # Don't remove next line

 # CT_INSERT_VERSION_STRING_BELOW

     default "5.5.2" if DMALLOC_V_5_5_2