- Fixed creating a new index name to be built on the new partition. (#1)

  The pg_part function attempts to create an index name, for the new
  partition to be built, from `indexdef' of the parent table.

  However, the initial pg_part release only supported simple indexes,
  built on the single column and no function.

  This fix is intended to accept multi-column indexes and function
  indexes for a new index name on the partition.

  Reported by pedroaxl.