swift234

Revert a combination of 11 commits

These commits are suspected of causing performance regressions:

r22995, "[stdlib] Array nil state elimination, part trois"
r22994, "[stdlib] Array nil-state elimination II"
r22993, "[stdlib] Array nil-state elimination I"
r22992, "[stdlib] Still more nil buffer elimination"
r22991, "[stdlib] Nix an unneeded typealias"
r22988, "[stdlib] Nix _ContiguousArrayBuffer._base, part deux"
r22986, "[stdlib] Kill _ContiguousArrayBuffer._base, part I"
r22985, "[stdlib] destroy redundant property"
r22975, "[stdlib] More array nil-state destruction"
r22974, "[stdlib] Construct HeapBuffer without AnyObject"
r22959, "[stdlib] non-nil ContiguousArray"

Swift SVN r23001