Bug 17261: Add memcached configuration info to about.pl

Bug 17261: Add memcached configuration info to about.pl

This patch adds a row in the About > System information tab, showing
the current configuration for memcached.

To test:
- Apply this patch, have memcached configured for the current instance (this is the
  default in kohadevbox)
- Make sure you have the memcached server running:
  $ sudo service memcached start
- Open the about page in the browser
=> SUCCESS: You get something like:
  Memcached:    Servers: 127.0.0.1:11211 | Namespace: koha_kohadev | Status: running
- Stop the memcached server:
  $ sudo service memcached stop
- Reload the about page
=> SUCCESS: You get something like
  Memcached:    Servers: 127.0.0.1:11211 | Namespace: koha_kohadev | Status: not running
- Set both MEMCACHED_* variables in the apache config for intranet the empty string:
  $ sudo vim /etc/apache2/sites-enabled/kohadev.conf
..
   SetEnv MEMCACHED_SERVERS ""
    #"127.0.0.1:11211"
   SetEnv MEMCACHED_NAMESPACE ""
    #"koha_kohadev"
..
- Restart apache:
  $ sudo service apache2 restart
- Reload the about page
=> SUCCESS: You get something like:
  Memcached:  Servers: undefined| Namespace: undefined | Status: unknown
- Sign off :-D

Sponsored-by: ByWater Solutions
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>