Convert vec::[mut_]slice to methods, remove vec::const_slice.
Convert vec::{head, tail, init, last} (and similar fns) to methods.
Convert vec::{pop, shift, unshift, insert, remove, swap_remove} to methods.
Convert vec::{push, push_all, push_all_move} to methods.
Convert vec::truncate to a method.
Convert vec::retain to a method.
Convert vec::{partition, partitioned} to methods.
Convert vec::{reserve, reserve_at_least, capacity} to methods.
extra: silence some test warnings.
std: silence some test warnings.
auto merge of #7430 : huonw/rust/vec-kill, r=thestinger