Implement an `address_insignificant` attribute

This can be applied to statics and it will indicate that LLVM will attempt to
merge the constant in .data with other statics.

I have preliminarily applied this to all of the statics generated by the new
`ifmt!` syntax extension. I compiled a file with 1000 calls to `ifmt!` and a
separate file with 1000 calls to `fmt!` to compare the sizes, and the results
were:

fmt           310k
ifmt (before) 529k
ifmt (after)  202k

This now means that ifmt! is both faster and smaller than fmt!, yay!
rustc: Obey RUST_MIN_STACK env var

A lot of people are hitting stack overflows in rustc. This will make it
easier to experiment with stack size.
syntax: Shrink enum Token and enum nonterminal

`enum Token` was 192 bytes (64-bit), as pointed out by pnkfelix; the only
bloating variant being `INTERPOLATED(nonterminal)`.

Updating `enum nonterminal` to use ~ where variants included big types,
shrunk size_of(Token) to 32 bytes (64-bit).

I am unsure if the `nt_ident` variant should have an indirection, with
ast::ident being only 16 bytes (64-bit), but without this, enum Token
would be 40 bytes.

A dumb benchmark says that compilation time is unchanged, while peak
memory usage for compiling std.rs is down 3%

Before::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.00user 0.39system 0:19.41elapsed 99%CPU (0avgtext+0avgdata 627820maxresident)k
    0inputs+28896outputs (0major+228665minor)pagefaults 0swaps
    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.64user 0.34system 0:32.02elapsed 99%CPU (0avgtext+0avgdata 629876maxresident)k
    0inputs+22432outputs (0major+229411minor)pagefaults 0swaps

After::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.07user 0.45system 0:19.55elapsed 99%CPU (0avgtext+0avgdata 609384maxresident)k
    0inputs+28896outputs (0major+221997minor)pagefaults 0swaps

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.90user 0.34system 0:32.28elapsed 99%CPU (0avgtext+0avgdata 612080maxresident)k
    0inputs+22432outputs (0major+223726minor)pagefaults 0swaps
auto merge of #8421 : alexcrichton/rust/unnamed-addr, r=thestinger

This can be applied to statics and it will indicate that LLVM will attempt to
merge the constant in .data with other statics.

I have preliminarily applied this to all of the statics generated by the new
`ifmt!` syntax extension. I compiled a file with 1000 calls to `ifmt!` and a
separate file with 1000 calls to `fmt!` to compare the sizes, and the results
were:

```
fmt           310k
ifmt (before) 529k
ifmt (after)  202k
```

This now means that ifmt! is both faster and smaller than fmt!, yay!
libsyntax: Update from `@Object` to `@mut Object` as required
librustc: Convert from `@Object` to `@mut Object` as needed
auto merge of #8420 : blake2-ppc/rust/shrink-token, r=cmr

`enum Token` was 192 bytes (64-bit), as pointed out by pnkfelix; the only
bloating variant being `INTERPOLATED(nonterminal)`.

Updating `enum nonterminal` to use ~ where variants included big types,
shrunk size_of(Token) to 32 bytes (64-bit).

I am unsure if the `nt_ident` variant should have an indirection, with
ast::ident being only 16 bytes (64-bit), but without this, enum Token
would be 40 bytes.

A dumb benchmark says that compilation time is unchanged, while peak
memory usage for compiling std.rs is down 3%

Before::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.00user 0.39system 0:19.41elapsed 99%CPU (0avgtext+0avgdata 627820maxresident)k
    0inputs+28896outputs (0major+228665minor)pagefaults 0swaps
    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.64user 0.34system 0:32.02elapsed 99%CPU (0avgtext+0avgdata 629876maxresident)k
    0inputs+22432outputs (0major+229411minor)pagefaults 0swaps

After::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.07user 0.45system 0:19.55elapsed 99%CPU (0avgtext+0avgdata 609384maxresident)k
    0inputs+28896outputs (0major+221997minor)pagefaults 0swaps

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.90user 0.34system 0:32.28elapsed 99%CPU (0avgtext+0avgdata 612080maxresident)k
    0inputs+22432outputs (0major+223726minor)pagefaults 0swaps
Add a field `borrow_offset` to the type descriptor indicating
what amount a T* pointer must be adjusted to reach the contents
of the box. For `~T` types, this requires knowing the type `T`,
which is not known in the case of objects.
Misc small cleanups
typeck/check/method: Remove `pub` from most methods
ty: Add (but do not yet use) AutoBorrowObject option to adjustments

Note: some portions of this commit written by @Sodel-the-Vociferous
(Daniel Ralston)
trans: Rely on new AutoBorrowObj adjustment to match up object receivers

Note: some portions of this commit written by @Sodel-the-Vociferous
(Daniel Ralston)
typeck: Modify method resolution to use new object adjustments, and
to favor inherent methods over extension methods.

The reason to favor inherent methods is that otherwise an impl
like

    impl Foo for @Foo { fn method(&self) { self.method() } }

causes infinite recursion.  The current change to favor inherent methods is
rather hacky; the method resolution code is in need of a refactoring.
borrowck: Integrate AutoBorrowObj into borrowck / mem_categorization

Also cleanup the treatment of mutability in mem_categorization, which still
included the concept of interior mutability. At some point, we should
refactor the types to exclude the possibility of interior mutability rather
than just ignoring the mutability value in those cases.
Update type visitor to use &Visitor and not @Visitor
tests: Add new tests for borrowck/objects and update some existing tests
Convert from transform to map
auto merge of #8455 : nikomatsakis/rust/issue-5762-objects-dralston-d, r=graydon

Fix #5762 and various other aspects of object invocation.

r? @graydon
auto merge of #8427 : brson/rust/rustc-stack, r=thestinger

A lot of people are hitting stack overflows in rustc. This will make it
easier to experiment with stack size.
Remove @io::Writer from sys/repr/reflect

At the same time, this updates the TyVisitor to use a mutable self because it's
probably going to be mutating state as it goes along anyway.