Bug 9239: Add syspref to enable QueryParser

Bug 9239: Add syspref to enable QueryParser

In light of the experimental nature of the QueryParser code at this
juncture, it behooves Koha to have the option of disabling QP, at least
for the purpose of comparing results between QP-enabled and QP-disabled
searches. This patch adds a UseQueryParser syspref to do just that. In
cases where the user enables QP without having QP installed, however,
there will be no dramatic failure, and Koha will simply fall back to
using the non-QP search code.

In order to reduce the overhead added by the introduction of QueryParser,
this patch adds a C4::Context->queryparser accessor to a static
QueryParser object which is initialized the first time it is required
and then reset thereafter.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Elliott Davis <elliott@bywatersolions.com>
Fixed merge conflict in sysprefs.sql and updatedatabase.sql

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Fixed merge conflict in sysprefs.sql und updatedatabase.pl
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>