mvcc: allow invoking maybe_merge_versions() inside allocating section
mvcc: allow invoking maybe_merge_versions() inside allocating section

Message-Id: <7316b4b8ce82889e4423607164ae1a0f6cee5194@scylladb.com>

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