flip.flip return self
Produce immutable.IndexedSeq where collection.IndexedSeq was produced before, e.g. Foldable#toIndexedSeq.
Merge pull request #437 from xuwei-k/request/flip-flip

flip.flip return self
Merge pull request #439 from S11001001/topic/immutable-seq-indexedseq

Produce immutable.IndexedSeq, not collection.IndexedSeq, in functions