Implement named constants in bindings
auto merge of #1914 : evilpie/servo/constants, r=Ms2ger

Generated code looks like this:

```rust
pub mod UIEventConstants {
  static SCROLL_PAGE_UP: i32 = -32768;
  static SCROLL_PAGE_DOWN: i32 = 32768;
} // mod UIEventConstants
```
Expose named constants in bindings.
Use 'NodeConstants' instead of magic numbers.
Use 'TConstants' instead of magic numbers.
auto merge of #1929 : saneyuki/servo/const, r=Ms2ger

We can use `TConstants` instead of by #1914 fixed.
Rust upgrades
Remove all traces of Box representation from bindings. Work around file read runtime problem.
Warning police.
Update submodules for warning police.
Rust upgrade for android
Rust upgrades
Make tests pass once more.
Check properly for None in the headless compositor case
Rust upgrade for new master rebase
make check bits of Rust upgrade