Prefix fragment types in inline.rs with `Inline`

This is to reduce confusion once we rename `servo::box_::Box` to `servo::fragment::Fragment`.
Convert usages of `Box` in type identifiers to `Fragment`
Rename functions, fields and adjust comments to use `fragment` instead of `box`

I tried to make sure to keep 'box' where it made sense, and alter comments so they still make sense.
Rename `box_.rs` to `fragment.rs`
Improve naming of structs in inline.rs
Improve line index documentation
Update submodules for EXT_DEPS dependency tracking.
auto merge of #2497 : bjz/servo/rename-box-type, r=pcwalton

I tried to make sure to keep 'box' where it made sense, and alter comments so they still make sense.

r? @pcwalton
Don't implement `ne` for ImageResponseMsg, since it matches the default.
auto merge of #2504 : zwarich/servo/dont-implement-ne, r=jdm
Fix unused_result warning in script_task
auto merge of #2503 : metajack/servo/ext-deps-redux, r=mbrubeck

@mbrubeck r?
Enable inline event handlers for XHR, and add most progressevent calls
auto merge of #2505 : Manishearth/servo/events-events-events, r=jdm

events events events!

Blocks #2282
auto merge of #2506 : Manishearth/servo/clickevent-warning, r=jdm
Add the 'direction' property and fix one RTL layout corner case.
Remove ConcurrentHashMap.

ConcurrentHashMap is unused and has a lot of uses of transmute_mut, so
it's best to remove it.
auto merge of #2508 : SimonSapin/servo/direction, r=pcwalton
JSRef<T> & Root<T> contains '*T' instead of RefCell.
auto merge of #2509 : zwarich/servo/remove-concurrent-map, r=pcwalton

ConcurrentHashMap is unused and has a lot of uses of transmute_mut, so
it's best to remove it.