swift234

Updated the playground transform's error handling.
Specifically, we now report type-checking errors in
added instrumentation to llvm::errs() and try to
restore the ASTs to their former state.

As Jordan points out, this requires a better and
more full solution, involving some form of AST
cloning or doing the playground transform at the
SIL level.  I have left in a TODO to that effect.

<rdar://problem/20444876>


Swift SVN r29798