switch field privacy as necessary

Struct fields are now private by default.
remove RefCell::get and RefCell::set

Rust PR #13301
c_types: allow lowercase type identifiers
use new proc bounds syntax

Changed in Rust 0.11-pre
test: change attribute syntax
use uint in byteswapping routines to sync with rust internals
add the `Allocator` trait
implement `Allocator` for `Heap`

Heap is a unit-like struct that represents the default allocator.
use the allocator interface with containers
add `default::Default`
allocators use Default
rfc
allocator: not required to impl Clone
Clone bounds. Required when necessary
remove ZeroAllocator
revive `forget` use
update allocator interface
FIXME: remove duplicate new, with_capacity
rm imports
FIXME: unused params