Bug 13729 - Give news in Opac a unique anchor

Bug 13729 - Give news in Opac a unique anchor

This patch introduces the use of the idnew-value from the opac_news table as a base for a unique anchor on each newsitem in Opac.

The anchor can be used for linking to specific newsitems and also for improving bug 7843 (RSS stream for news) with a unique link to each item in the RSS stream.

Test plan:
* Make shure you have a few news in the opac. Best is if it's enough to hide a few beneath the bottom of the window.
* Install the patch.
* Verify that you can access newitems with links like mykoha/cgi-bin/koha/opac-main.pl#newsitem4
* Experiment with removing newsitems and verify that that the newsitem-id stay unique to each newsitem.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Works as advertised. Nice enhancement!

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
(cherry picked from commit 13a16343fa21e87b9c4723fdf4d02ae6eb46d495)
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>