swift234

Type-check string interpolations with the StringInterpolationConvertible protocol.

Previously, string interpolation mapped down to a sequence of +
operations on strings. Instead, introduce the
StringInterpolationConvertible protocol, which takes an array of
strings and produces a string. Note that only the new type checker
uses this approach.

Make String conform to the StringInterpolationConvertible protocol. 

Fixes <rdar://problem/11539912>.

swift.swift now sends all of its coercions through the new type checker.


Swift SVN r5110