This decreases total testing time by over a minute on my old Mac Pro.
It probably has much less effect on systems with fewer cores, but shouldn't
be any worse there.
Swift SVN r22745
...because their semantics were unclear. The new idiom is explicit
construction of the target type using the "bitPattern:" argument label:
myInt.toUnsigned() => UInt(bitPattern: myInt)
Fixes <rdar://problem/17000821>
Swift SVN r20479