swift234

[stdlib] Don't expose uninitialized memory

...at least, not without the word "unsafe."  ManagedBuffer's create()
function takes a closure that creates an initial value for its "value"
property (which is technically computed but effectively stored).  Before
this change, the closure had access to that property before it was
initialized.  Now you can still get there, but you have to go through
"withUnsafeMutablePointer*" methods.

Swift SVN r22501