clustering_row: Add apply() overload
clustering_row: Add apply() overload

This patch adds an overload to the apply() function,
which takes a clustering_row by reference, to copy. This will be
needed by future patches, when merging base table updates with the
existing data.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <1482881106-3202-1-git-send-email-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

avikivity/scylla,scylladb/scylla,duarten/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla