remove issue #3148 workarounds (no longer needed)
treemap: get rid of some implicit vector copies
get rid of implicit vec copies in treemap iterator

Each call to next() was doing a copy rather than a move. There's
currently no way for this to be a method that uses &mut self, so it has
to be a free function. Closes #4763.
update treemap FIXME
treemap: make map_next and set_next public
remove old snapshot workaround from smallintmap
auto merge of #4815 : thestinger/rust/treemap, r=pcwalton

5283a8b reworks the TreeMap lazy iterator to use `&mut` again, which closes #4763. It gets the performance of the set methods back in the same ballpark that it was pre-INHTWAMA which is nice. These can be turned back into methods eventually.

e5b6334 removes the transitional smallintmap attributes which closes #4737.