[PATCH] Implement CapturedStmt AST

[Wei Pan]

  Thanks for the suggestions! This updated patch removed "CopyExpr' from the Capture class. Similar to LambdaExpr, field initializer expressions will be stored in CapturedStmt instead.

  Removed ASTDumper::VisitCapturedStmt since CapturedStmt::children consist of field initializers and the statement being captured, as stated in the comment.

  Thanks again for reviewing this patch!

http://llvm-reviews.chandlerc.com/D370