auto merge of #12697 : thestinger/rust/vec, r=huonw

This exists for the sake of compatibility during the ~[T] -> Vec<T>
transition. It will be removed in the future.

diff --cc src/librustc/lib.rs
Simple merge

diff --cc src/libstd/vec_ng.rs
Simple merge

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