Bug 13188: (RM follow-up) Several fixes on db changes

Bug 13188: (RM follow-up) Several fixes on db changes

Several issues with the atomic update:
 - File must to be .pl
 - File must be executable : chmod a+x
 - Syspref type is 'free' not 'multiple'

Small addition in atomic update:
I've added a print of syspref name and value,
this can be usefull for upgrade logs.

Also a minor issue in installer/data/mysql/mandatory/sysprefs.sql :
The description whas different from the atomic update.
I choose that atomic update is correct.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>