swift234

Completed my changes to the playground transform
to support brace entry/exit.  We now maintain a
stack of brace statements we know we're inside.
The elements of this stack are colored:

- If we encounter a loop, while we are walking
  that loop we color its container to indicate
  that "break" and "continue" exit all braces
  up until the container of the loop.

- If we encounter a function, while we are
  walking that function we color its container
  to indicate that "return" exits all braces
  up until the container of the function.

Since at this point every BraceStmt is modified,
we don't need the "Modified" flag and I excised
it.


Swift SVN r16230