Upgrade to latest Rust.
Merge pull request #2725 from metajack/rustup-20140624

Upgrade to latest Rust.
Remove generate_cacheable_wrapper_characterdata!
Remove generate_cacheable_wrapper!
Remove generate_cacheable_wrapper_node!
Remove generate_cacheable_wrapper_htmlmediaelement!
Remove generate_cacheable_wrapper_htmltablecellelement!
Remove generate_cacheable_wrapper_htmlelement!