fix arm stack alignment
fix issue #6209
auto merge of #6667 : crabtw/rust/arm-rt, r=brson

This fixes segmentation fault of new rt tests.
For example
```
use core::rt::test::*;
use core::rt::comm::*;
use core::cell::Cell;

fn main() {
    do run_in_newsched_task {
        let (port, chan) = oneshot::<~int>();
        let port_cell = Cell(port);
        do spawntask_immediately {
            assert!(port_cell.take().recv() == ~10);
        }
        chan.send(~10);
    }
}
```
"Type :help for help", similar to ghci
Fix #6342
auto merge of #6671 : kud1ing/rust/patch-1, r=z0w0
Implement static_assert attribute

This verifies that a static item evaluates to true, at compile time.
Add static_assert doc blurb
auto merge of #6670 : cmr/rust/static_assert, r=graydon

This verifies that a static item evaluates to true, at compile time.
auto merge of #6672 : yjh0502/rust/fix_6342, r=graydon

Fix #6342
testsuite: Add passing test for #4107
testsuite: Make main fn public
auto merge of #6483 : catamorphism/rust/issue-4107, r=catamorphism
Fix ICE in macros
Add test
auto merge of #6686 : cmr/rust/fix-6596, r=catamorphism

The error message is extremely unideal.
auto merge of #6669 : yjh0502/rust/fix_6209, r=graydon

Fix issue #6209, and some related issues about constant expression
 - unmatched type between arms
 - unmatched type in range
WIP segfaulting POS