stdlib: Mark many higher-order function interfaces as 'rethrows'.

This covers:

- Lifetime-extending wrappers, like withExtendedLifetime, withCString, and withUnsafe*Pointer
- 'map' and friends on Optional
- 'indexOf'

A few APIs I haven't gotten to yet in this first pass:

- Autoclosure APIs, like assert, &&, etc.
- the 'isOrderedBefore' predicate for sorting APIs. The sorting implementation does some microoptimizations with 'inout' closures that violate rethrows checking.
- Strict 'map', 'filter', and friends on CollectionType. These need some plumbing in Lazy to be able to thread a Result-forming transformation through.

This version of the patch updates some protocol customization implementations that I missed the first time around, and includes the tests I forgot to add in the previous iteration.

Swift SVN r30790

stdlib/public/core/CollectionAlgorithms.swift.gyb

@@ -57,10 +57,10 @@ extension CollectionType {
   ///
   /// - Complexity: O(`self.count`).
   public func indexOf(
-    @noescape predicate: (${GElement}) -> Bool
-  ) -> Index? {
+    @noescape predicate: (${GElement}) throws -> Bool
+  ) rethrows -> Index? {
     for i in self.indices {
-      if predicate(self[i]) {
+      if try predicate(self[i]) {
         return i
       }
     }