auto merge of #1626 : kmcallister/servo/flowlist, r=pcwalton

r? @pcwalton

Some points of concern:

* Is this really memory-safe? Is there a way to access a stale `Rawlink` that doesn't exist in the normal `DList` code?
* Is it okay to coerce both `~Flow` and `&Flow` to `(uint, uint)` (or the moral equivalent) and compare them?  Will a given `Flow` always have the same (obj, vtable) regardless of whether it's obtained through `~Flow` or `&Flow`?
Implement document.characterSet

Spec:
http://dom.spec.whatwg.org/#dom-document-characterset

This is a sub-task for #1428.
auto merge of #1604 : brunoabinader/servo/document-characterset, r=Ms2ger

Spec:
http://dom.spec.whatwg.org/#dom-document-characterset

This is a sub-task for #1428.
layout: Lazily create boxes for whitespace, speculating that they won't
be needed.

33% win in flow construction on the rainbow page.
auto merge of #1630 : pcwalton/servo/short-circuit-whitespace, r=larsbergstrom

be needed.

33% win in flow construction on the rainbow page.

r? @larsbergstrom
Implement ProcessingInstruction DOM interface

Spec:
http://dom.spec.whatwg.org/#interface-processinginstruction

Closes #1619.
auto merge of #1620 : brunoabinader/servo/dom-processinginstruction, r=Ms2ger

Spec:
http://dom.spec.whatwg.org/#interface-processinginstruction

Closes #1619.
Build libstd etc. with debug info when Servo configured with --enable-debug
Remove some string literal heap allocations
Change the mechanism behind summit-crash.html
Move FailureMsg contents into a cloneable struct
Add a helper for sending a message on task failure
wip
more wip