secondary index: fix indexing of partition-key column
secondary index: fix indexing of partition-key column

Indexing an only partition key component is not allowed (because it would
be redundant), but it should be allowed to index one of several partition
key components. We had a bug in that case: the underlying materialized view
we created had the same column as both a partition key and a clustering
key, which resulted in an assertion failure. This patch fixes that.

Fixes #3404.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20180501121544.22869-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

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