Added the bootstrap_priv library.

This library contains functions to emulate the (known) functionality of the contents of the private bootstrap_priv header.
Renamed libbootstrap_priv to libsb-bootstrap.

I am doing this because this library will also contain functions that wrap Mach bootstrap functionality to work correctly with sandboxing. These functions will be added in a later commit.
libsb-bootstrap now contains sandbox-safe bootstrap APIs.
CoreFoundation now links against libsb-bootstrap.
Removed private API reference in CFSortFunctions.c.
CFUserNotification now uses libsb-bootstrap.
Removed private API use from CFMachPort.c.
Corrected the declaration of the bootstrap_priv functions.
Removed private API use from CFMessagePort.c
Removed private API use from CFUtilities.c.
Added a file I forgot in 594a05c53a08.
Removed private API use from CFBundle.c.
Removed private API use from CFPlatform.c.
Removed private API use from CFRunLoop.c.
Removed private API use from CFURLPriv.h.