swift234

stdlib: Add 'rethrows' to more SequenceType and CollectionType algorithms.

Including:

- forEach
- split
- Optional flatMap
- minElement
- maxElement
- startsWith
- elementsEqual
- lexicographicalCompare
- contains
- reduce

Still not touching 'map', 'filter', 'flatMap', or 'sort', which need various levels of rearchitecting to fix.

Swift SVN r30792