TransformKohaToMarc enhancement

TransformKohaToMarc enhancement

TransformKohaToMarc function is called for each biblio and item that has
to be build. This function execute a DB statement for each Koha field
that has to be mapped to a MARC tag/letter. This impact deeply
performances for script like rebuild_zebra, especially since items are
not anymore in bilio records and have to be rebuild on the fly.

I'm proposing a patch which read Koha field to MARC field mapping just
one time and cache it. My test show a 30% execution time improvement on
rebuild_zebra.pl script. It uses already cached mapping in C4::Context.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
http://bugs.koha-community.org/show_bug.cgi?id=6990
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
(cherry picked from commit 02d392a502571e14df9373782343cf5e3bbe83b6)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>