Remove unused code path - simplifies other refactoring.
Suppress the compiler warning about raw_pointer_deriving in layout/context.rs.

This suppress the following compile warning:
```
compile: servo
src/components/main/layout/context.rs:75:18: 75:26 warning: use of `#[deriving]` with a raw pointer, #[warn(raw_pointer_deriving)] on by default
src/components/main/layout/context.rs:75     pub stylist: *Stylist,
                                                          ^~~~~~~~
```
Treat 'native-threading' option correctly.
Remove the long-hand handling about 'native-threading' option.
Ignore dirty submodules for fontconfig and libexpat
Merge pull request #2716 from Manishearth/die-fontconfig-die

Ignore dirty submodules for fontconfig and libexpat
Partial implementation of FormData and File
Merge pull request #2559 from Manishearth/formdata

Partial implementation of FormData and File
Update the test results for DOMTokenList / Element.classList.
Disable tests that require the iframe load event.
Disable SVG tests.
Update remaining web-platform-tests results.
Merge pull request #2717 from Ms2ger/wpt-exp

Update web-platform-tests expectations.
Merge pull request #2713 from glennw/font-cleanup-2

Remove unused code path - simplifies other refactoring.
Merge pull request #2715 from saneyuki/fix_opt

Treat 'native-threading' option correctly.
Merge pull request #2714 from saneyuki/fix_warn

Suppress the compiler warning about raw_pointer_deriving in layout/context.rs