Bug 18336: Add explicit index names to kohastructure.sql

Bug 18336: Add explicit index names to kohastructure.sql

This patch just adds an explicit index name to the search_marc_map
table. The atomicupdate on this patchset is a good example of why we
better have them.

Sponsored-by: Hotchkiss School
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>