std: more dummy type parameters on iterators to work around #6967.
std: remove vec::each2 and vec::each2_mut in favour of iterators
std: remove each[i]_mut functions, in favour of iterators.
Merge branch 'each-fn-kill' of https://github.com/huonw/rust into each-fn-kill
iterator: work around method resolve bug (#5898)
auto merge of #6999 : thestinger/rust/each-fn-kill, r=thestinger