libcollections: use unboxed closures in `Bitv` methods
libcollections: use unboxed closures in `Vec` methods
libcollections: use unboxed closures in `DList` methods
libcollections: use unboxed closures in `[Clone]SliceAllocPrelude` methods
libgraphviz: fix fallout
libcollections: use unboxed closures in `VecMap` methods