We no longer create intermediate NSString copies to compare and hash swift
Strings. Instead we call directly into the ICU library.
I measured a 1.2 to 2x improvement on dictionary benchmarks as a result of this.
The SuperChars benchmark is also about 1.2x faster because of this.
Pure ASCII comparison has gotten a little bit slower (20% on a pure comparison
micro-benchmark) because we no longer do a memcmp. Doing a memcmp on ASCII is
not the same as the default unicode collation. Instead we have to a string scan.
The default unicode collation does not order like ASCII does and ignores
characters (for example the \0 character).
rdar://18992510
Swift SVN r31474
