rm FIXME from LinearMap's to_bucket

There are no more poor hash functions left in the codebase, and it makes
sense to rely on there being a good hash function thanks to the
inclusion of SipHash and the ease of using it with custom types.

Closes #3041
rt: rand.rs expects rust_next() to return uint32_t, not size_t
move isaac RNG utility functions to new rust_rng.cpp file
encapsulate isaac RNG in rust_rng struct
reseed rust_rng after generating 32KB
don't deplete RNG entropy when there is only one runnable task
add reserve_at_least method to LinearMap/LinearSet
libstd: Get rid of `move`.
libstd: Fix broken test.
libcargo: Get rid of `move`.
librustdoc: Get rid of `move`.
libcore: Get rid of `move`.
compiletest: Get rid of `move`.
librustc: Get rid of `move`.
libsyntax: Get rid of uses of `move` and don't parse it.
tests/tutorials: Get rid of `move`.
libsyntax: Remove move as a keyword.
auto merge of #4958 : cpeterso/rust/reseed-rng, r=graydon

For Issue #4709:

**c531506 rt: rand.rs expects `rust_next()` to return `uint32_t`, not `size_t`**

rand.rs expects `rustrt::rand_next()` to return `u32`, but the `rand_next()` C function returns `size_t`: https://github.com/mozilla/rust/blob/ca71c6ec5bb8106121cbe33eec5a6a9ca7786039/src/libcore/rand.rs#L34

**f4320b6 move isaac RNG utility functions to new rust_rng.cpp file**
**665e900 encapsulate isaac RNG in `rust_rng` struct**

Move isaac's `randctx` into a `rust_rng` struct to make names similar to `rand::Rng` function names and prepare for auto-reseeding in the next commit.

**9a78dc9 reseed `rust_rng` after generating 32KB**

Precedents from other languages:
* Haskell's `GenAutoReseed` generator reseeds itself after generating 32KB: http://hackage.haskell.org/packages/archive/DRBG/0.1.2/doc/html/Crypto-Random-DRBG.html#t:GenAutoReseed

* Go's RNG reseeds itself after generating 1MB: https://code.google.com/p/go/source/browse/src/pkg/crypto/rand/rand_unix.go?name=go1.0.3#94

**9a76d71 don't deplete RNG entropy when there is only one runnable task**

`rust_sched_loop::schedule_task()` unnecessarily calls `isaac_rand()` for the common case when there is only 1 runnable task, thus depleting RNG entropy and incurring unnecessary overhead.
auto merge of #4959 : thestinger/rust/map, r=graydon
auto merge of #4964 : luqmana/rust/demove, r=graydon

As per #4339/#3676 this pull removes all uses `move` and gets rid of parsing it in libsyntax.
So that's one more thing to cross off #4707