Update iter with &self and passing around references

[erickt]

This also fixes a couple warnings, and un-xfails two iter-related tests.

[brson]

Everything looks ok to me except the last commit. Adding implementations of the iter traits for ~[T] and @[T] makes a lot of redundancy. What is the problem that this fixes?

Would be great if @nikomatsakis could review.

This bug is vaguely related, in that it is about making other vector types work with &[T] impls: #4148.

[brson]

I merged the first 3.

[erickt]

#4148 looks like the exact problem I was running into. I could not get vec::flat_map_to_vec to compile without defining an implementation of iter::BaseIter for ~[T]. Could we tag these redundant impls with a FIXME #4148: ... for the 0.5 release, and remove them when #4148 is fixed?

[brson]

I agree.

[erickt]

Merged in, closing.