Fix #1480, added -D unused-imports to rustc flags
Pass Option<T> for optional primitive arguments without a default value (fixes #1813).
Clean files associated with static linking
auto merge of #1941 : larsbergstrom/servo/clean_rlib, r=metajack

Three things changed with the `make clean` process:
- Remove the *.rlib files associated with the Servo crates
- Remove the libservo-*.a file, which we will (Very Soon Now) generate now on Android instead of a .so
- Update all the submodules, which have corresponding *.rlib file cleanup changes
auto merge of #1909 : Ms2ger/servo/optional-defaults, r=jdm

...(fixes #1813).
auto merge of #1939 : khodzha/servo/unused_imports, r=jdm

Attempt to fix #1480. I have no idea what I'm doing
Force infallible binding methods to return void.(fixes #1933)
Rename squirrel_away_unboxed to squirrel_away_unique.(fixes #1938)
auto merge of #1944 : lpy/servo/issue1938, r=Ms2ger

see #1938
Pass the isDefinitelyObject argument to wrapObjectTemplate and fix nearby whitespace (fixes #1196).
auto merge of #1945 : Ms2ger/servo/1196-isDefinitelyObject, r=jdm

... and fix nearby whitespace (fixes #1196).
auto merge of #1943 : lpy/servo/issue1933, r=jdm

see #1933
Split TCast::to into TCast::to_unchecked and TCast::to.
auto merge of #1864 : saneyuki/servo/split_cast_to, r=jdm

fix #1836
Change from TNode/TElement::with_element() to as_element().
auto merge of #1867 : saneyuki/servo/1828, r=pcwalton

Fix #1828
Move attributes-related functions onto JS<Element>.
auto merge of #1913 : Ms2ger/servo/attributes, r=jdm
Remove unused import of std::intrinsics::uninit.
Remove the preSuccess and postSuccess arguments to getJSToNativeConversionTemplate.

They were used for unions until 06f9afdad52cba426aedd45d0e08a7b2bdecc8f4.