librustc: Lots of de-muting. rs=demuting
libsyntax: De-mut TtFrame
libsyntax: Use more @self in diagnostics
libsyntax: De-mut the handler and span handler
libsyntax: De-mut TtReader and StringReader
libsyntax: De-mut the pretty printer
libsyntax: De-mut ext ctxt
libsyntax: De-mut the AST map
librustc: De-mut regionck.
librustc: De-mut the borrow check
auto merge of #4792 : pcwalton/rust/demuting, r=pcwalton