auto merge of #16468 : pcwalton/rust/as-renaming-import, r=alexcrichton

The old syntax will be removed after a snapshot.

RFC #47.

Issue #16461.

r? @brson

diff --cc src/libsyntax/ast.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge

diff --cc src/libsyntax/print/pprust.rs
Simple merge