swift234

[stdlib] UTF16View: unavailable subscript with Int

There had been some discussion of making this available iff Foundation
is loaded, but it turns out that there are almost no Foundation APIs
that return NSUInteger indices into NSStrings without first packaging
them into NSRanges, and when <rdar://problem/19255291> is addressed,
these NSRanges will become Swift Range's, which have a different
interface.  So there's no seamless API transition to be had here, for
any substantial subset of code written against Cocoa.

Swift SVN r23949