[PATCH] Initial SEH IR generation implementation

[Alexey Bataev]

> He feels that CapturedStmt is an implementation artifact that shouldn't be in the AST because it doesn't reflect anything user-written.
Actually, initially this class was designed to be a basic class for other statements, which may require function outlining. But Doug Gregor recommended to make it a separate statement.

http://reviews.llvm.org/D5607