Get availability annotations right for NSCocoaError.
Get availability annotations right for NSCocoaError.

Fix the script to not wantonly drop availability annotations, and
update NSCocoError accordingly. Also drop in a reinterpret-casting
rawValue initializer, which matches what we get when importing enums
from C.

Swift SVN r28563

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation