Bug 13087: Add a notice for use_zebra_facets problems in about page

Bug 13087: Add a notice for use_zebra_facets problems in about page

This patch adds two checks to about.pl:

- use_zebra_facets entry presence in koha-conf.xml
- use_zebra_facets==1 and zebra_bib_index_mode==dom

The idea is to alert the user if it has conflicting or wrong settings. Even
if there's a fallback to a working configuration.

To test:
- On clean master install, go to the about page
=> SUCCESS: No warnings regarding use_zebra_facets
- Comment out the use_zebra_facets entry, reload
=> SUCCESS: The about page mentions the use_zebra_facets entry is missing
- Uncomment the use_zebra_facets entry, make sure it is set to 1
- Change zebra_bib_index_mode to 'grs1', reload
=> SUCCESS: The about page says zebra_bib_index_mode is not set to DOM even though
  you have use_zebra_facets set.
- Sign off :-D

Regards
To+

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Followed test plan with success

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, tested by changing the koha-conf.xml file.
Note: There is no warning if use_zebra_facets is 0.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>