Added filtered method for Option type
auto merge of #7279 : hanny24/rust/master, r=msullivan

This commit adds filtered method for Option type. It is not exactly necessary (chain method can be used instead), however I believe that this approach using extra filtered method is more convinient.
remove old_iter

the `test/run-pass/class-trait-bounded-param.rs` test was xfailed and
written in an ancient dialect of Rust so I've just removed it

this also removes `to_vec` from DList because it's provided by
`std::iter::to_vec`

an Iterator implementation is added for OptVec but some transitional
internal iterator methods are still left
Fix/annotate a variety of xfails
xfail tests again for now (issues #7336, #7340)
deal with windows
implement Clone for slices
iterator: implement `collect` with FromIterator

This makes it take advantage of the size hint for pre-allocation.
xfail-pretty on un-xfailed test