swift234

Test that the remangler round-trips successfully.

To get this to work, delay some "cleanup" work in the
demangler.  For example, we now preserve in the tree
whether something was mangled as an allocating
initializer, and we only special-case the class vs.
non-class cases in the pretty printer.

Also fixes a number of remangling bugs, of course.

Swift SVN r24534