Bug 7847: OPAC search dies with Plack

Bug 7847: OPAC search dies with Plack

Due to a dependency cycle between C4::Search and C4::Items, searches
in the OPAC die spectacularly under Plack. This counter-patch extends
dpavlin's solution and replaces use with require for C4::Search in
C4::Items and for C4::Items in C4::Search.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>