core: remove iter_bytes helper functions
cleanup warnings from libstd
cleanup warnings from libextra
cleanup warnings from libsyntax
cleanup warnings from librustc
cleanup warnings from librusti
cleanup warnings from librustdoc
cleanup warnings from compiletest
cleanup warnings from librustpkg
Fix some std/extra language in the tutorial
auto merge of #6690 : erickt/rust/cleanup-warnings, r=brson

Simple patch series to fix up all the warnings a rustc compile is giving at the moment. It also fixes a NOTE in `to_bytes.rs` to remove the `to_bytes::iter_bytes_<N>` functions.