swift234

Reimplement the AST, Sema, and SILGen of defer to be closure based.
Now we bind the defer body into a ClosureExpr and emit it at the point of
the defer.  At any exit points out of the controlled region, we emit a call 
to the closure.

This should cover any problems where expressions cannot be emitted multiple times.
However, this is dramatically more complex than the obvious implementation, so I 
hope this patch can be reverted.



Swift SVN r27767