std: Rename Iterator adaptor types to drop the -Iterator suffix

Drop the "Iterator" suffix for the the structs in std::iterator.
Filter, Zip, Chain etc. are shorter type names for when iterator
pipelines need their types written out in full in return value types, so
it's easier to read and write. the iterator module already forms enough
namespace.
New naming convention for ast::{node_id, local_crate, crate_node_id, blk_check_mode, ty_field, ty_method}
mk: Fix NO_REBUILD so stdtest can be tested without re-bootstrapping. Closes #8101
mk: Rename CTEST_BENCH to TEST_BENCH

The CTEST prefix is specifically related to the compiletest driver
mk: Add NO_BENCH variable for turning off the --bench flag
Remove ChanOneHack/PortOneHack extra allocation
Optimize try_recv to not require the two context switches when data is available.
Adding an initial description to vec.rs.

Let's explain more of what this module is about, not just 'vectors.'
auto merge of #8090 : blake2-ppc/rust/iterator-adaptor-names, r=pcwalton

Drop the "Iterator" suffix for the the structs in std::iterator.
Filter, Zip, Chain etc. are shorter type names for when iterator
pipelines need their types written out in full in return value types, so
it's easier to read and write. the iterator module already forms enough
namespace.
Add some missing method wrappers to std::num
Improve std::num module description, and fix some formatting
iterator: implement DoubleEndedIterator for FlatMap
iterator: implement size_hint() for FlatMap
std: Implement RandomAccessIterator for iterator adaptors

Implement RAI where possible for iterator adaptors such as Map,
Enumerate, Skip, Take, Zip, Cycle (all of the requiring that the adapted
iterator also implements RAI).
std: Tests for RandomAccessIterators
std: Remove RandomAccessIterator impl for VecMutIterator

The RandomAccessIterator implementation is not sound for the mutable vec
iterator, and makes it easy to duplicate &mut element pointers.
extra: Implement DoubleEnded and RandomAccess iterators for bitv
extra: Implement RandomAccessIterator for RingBuf
extra: Implement iterator::Extendable
std: Implement Extendable for hashmap, str and trie