Bug 11478: Replace experimental given/when keywords

Bug 11478: Replace experimental given/when keywords

The keywords given and when are flagged experimental
in perl 5.18 and subject to change. This patch
replaces the construct by an if/elsif

To test:

[1] Verify that prove -v t/SimpleMARC.t passes.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 08d15a6fd1b51435b92f1056f6735c8317636068)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>