streamed_mutation: do not leave mutation in an invalid state
streamed_mutation: do not leave mutation in an invalid state

This patch avoids moving entries from range tombstones and clustering
rows sets in streamed_mutation_from_mutation(). Such action breaks these
sets as the entries will be left in some unknown state.

Instead, the sets are being broken in a supported and predictable way
using unlink_leftmost_without_rebalance().

Signed-off-by: Paweł Dziepak <e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>
Message-Id: <1468843205-18852-1-git-send-email-e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>

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