Bug 16993: Fix CSRF in memberentry.pl

Bug 16993: Fix CSRF in memberentry.pl

If an attacker can get an authenticated Koha user to visit their page
with the url below, they can change patrons' passwords or other
patrons'details

members/memberentry.pl?op=save&destination=circ&borrowernumber=3435&password=ZZZ&password2=ZZZ&nodouble=1

Test plan:

Trigger
members/memberentry.pl?op=save&destination=circ&borrowernumber=42&password=ZZZ&password2=ZZZ&nodouble=1

=> Without this patch, the password will be updated
=> With this patch applied you will get a crash "Wrong CSRF token" (no
need to stylish)

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Amended: removed the commented use Digest::MD5-line.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>