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
A revamped version of HeapBuffer that doesn't allow null buffer
references. Something like this is needed for killing the null array
state.
Swift SVN r22683
Make unique reference checking available to users, making ManagedBuffer
a complete facility for building COW value types. Also rationalize the
way we name and organize the runtime primitives we ultimately call.
Swift SVN r22594
