Closes #12386. Removed 'pub mod' doc-comments in std::io's mod.rs file. Added summary doc-comments to test.rs, util.rs and stdio.rs.
rustc: Explicitly mention type params with missing `'static` bounds

Also renames `check_durable` to `check_static` and removes the outdated
comment.
auto merge of #12490 : zslayton/rust/doc-fix-12386, r=alexcrichton

Attn: @huonw 

Addresses #12386.
auto merge of #12572 : lifthrasiir/rust/owned-ptr-static-bound, r=alexcrichton

This is inspired by the [question](http://www.reddit.com/r/rust/comments/1yy57k/unsolved_question_from_irc/) (re-)posted to /r/rust. The error message in this question correctly states that one should add `'static` to the trait bounds, but does not state which trait bounds. This PR makes that explicit by appending two words.

This also renames `check_durable` to `check_static` and removes the outdated comment as a cleanup.
fs: use an iterative algorithm for 'mkdir_recursive'

as requested in #6109
fs: use an iterative algorithm for 'rmdir_recursive'