Add lru_cache to libextra
Disable priv in std::comm::Port, etc

It's useful to allow users to get at the internal std::rc::comm::Port,
and other such fields, since they implement important traits like
Select.
Fix up mingw64 target.
mk: Get rid of redundant LIBUV_FLAGS.
Introduce Mut<T> to libstd

Based off of blake2-ppc's work in #9429.
Remove RcMut

Rc<Mut<T>> should be used instead
Move Rc tests away from Cell
Cell -> Mut switch in comm
Make MutRef more consistent with &mut
Change Mut::map to Mut::with
Strip down Cell functionality
More Mut tests
Add Rc::from_mut
Remove sjlj stuff from rust_upcall and don't pass -Werror to libuv.
Add ctype-likes to Ascii
auto merge of #10611 : cmr/rust/ascii_flesh, r=pcwalton

These are super boring. I can add tests if really desired, but they'd be long
and even more boring than the methods.
Use CXX not CC for linking.
Use linker optimizations on Linux
Move mutable::Mut to cell::RefCell
extra: improve the errors for the JSON Decoder.

Fixes #4244.