swift234

stdlib: _copyToNativeArrayBuffer(): use unsafe more

Now we initialize the array buffer from sequences using unsafe pointer
arithmetic, which avoids extra retain/release traffic.  But since the
size of the sequence is not known in advance, we only initialize as much
as underestimateCount() promises, and fall back to the slow approach for
the tail.  Nevertheless, for collections, where the size is known
precisely, this technique is suboptimal only by one branch.

rdar://20530390

Swift SVN r27380