swift234

stlib: Introduce a LifetimeManager -- a class to emulate precise lifetime.
This is needed to ensure that the objects are not deallocated when they are
passed as UnsafePointers to C APIs.

Also clean up our String <-> CString <-> UnsafePointer<UInt8> conversion
routines.  Clean up all users and refactor users poking into CString's
internals whenever possible.


Swift SVN r5656