Bug 20000: Use Modern::Perl in installer scripts

Bug 20000: Use Modern::Perl in installer scripts

To test:

Check that we are using Modern::Perl when strict *and* warnings were used before,
and commented lines and FIXMEs have been removed from the rest, out of
files listed below.

data/mysql/backfill_statistics.pl
data/mysql/labels_upgrade.pl
data/mysql/patroncards_upgrade.pl
data/mysql/update22to30.pl
data/mysql/updatedatabase.pl
externalmodules.pl
html-template-to-template-toolkit.pl
install.pl

Sponsored-by: Catalyst IT
Signed-off-by: Maryse Simard <maryse.simard@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>