libstd: Add some functionality to `Vec<T>`
libsyntax: Mechanically change `~[T]` to `Vec<T>`
libsyntax: Fix errors arising from the automated `~[T]` conversion
librustc: Fix errors arising from the automated `~[T]` conversion
librustdoc: Fix errors arising from the automated `~[T]` conversion
libfourcc: Fix errors arising from the automated `~[T]` conversion
auto merge of #12637 : pcwalton/rust/devecing, r=alexcrichton

r? @alexcrichton