indexing - explicitly pass previous record to ModZebra

indexing - explicitly pass previous record to ModZebra

Because NoZebra indexing requires having both
the old and new versions of a record when processing
an updated, I adjusted the ModZebra sub to require
that the old version be explicitly passed to it.
That way, the zebraqueue row (for Zebra mode) can
now be added *after* the biblio and biblioitems
updates have been completed.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>