libcore: Change `[const T]` to `const [T]` everywhere
libsyntax: Stop parsing `[const T]`.
librustc: Remove all uses of the old `[T * N]` fixed-length vector syntax
librustc: Stop parsing `[T * N]`.
librustc: Fix bug with newtype structs containing dtors
auto merge of #5534 : pcwalton/rust/newtype-struct-with-dtor, r=jld

r? @jld (last commit)

Testcase should make it obvious, but there were a couple of assertions in trans that are wrong in the presence of newtype structs with destructors.

This was blocking sprocketnes.