The "_specs" array contains column specifications that have the bind
marker name if there is one. That results in
get_partition_key_bind_indices() not being able to look up a column
definition for such columns. Fix the issue by keeping track of the
actual column specifications passed to add() like Cassandra does.
Fixes#2369
Message-Id: <1494397358-24795-1-git-send-email-penberg@scylladb.com>