Add an HTML file where JavaScript changes text color

I wanted this for testing incremental layout, but it's also useful to
illustrate a bug I just found.
debug: Send flow tree dump to stderr for consistency
Fail the script task when page URL load fails

It's confusing that specifying a nonexistent file on the command line just
gives me a blank page.  Until we have a real 404 page let's just crash.
Reflow and redisplay after script timers fire

We don't know what the script changed.  This will be less painful with
incremental layout.

Fixes a crash from calling reflow() with self.damage = None.
Update rust-png pointer.
auto merge of #618 : kmcallister/servo/test-html, r=jdm,jdm

I wanted this for testing incremental layout, but it's also useful to illustrate a bug I just found.

(PR attempt #2, hopefully Bors won't flip out this time)
auto merge of #619 : kmcallister/servo/script-redisplay, r=jdm

Stuff I found in the process of working on incremental layout.
auto merge of #620 : sonwow/servo/bindings, r=jdm

It's just a part of bingings for Document.
Autogenerate DOM bindings for Document.
auto merge of #627 : jdm/servo/docgen, r=kmc,jack
structural changes to support Iframes
handle pipeline exiting properly
navigation bug fix
switched window.page from *mut Page to @mut Page
removed a call to copy in servo.rc and renamed NavigationContext.navigate ==> NavigationContext.load
remove unused arg from script_task::handle_navigate_msg

remove unnecessary commented-out code
fix borrow check failures by reverting to storing *mut Page in window
updated rust-http-client submodule
auto merge of #628 : tkuehn/servo/master, r=metajack

Completed:
  * Replace pipeline navigation context with frame tree navigation context
  * Reuse script task for same origin iframes
  * Block on size future for iframe reflow
  * Remove global script context
  * Change codegen to use specific page context rather than script context.

Still to do:
  * Compositor's handling of relative frame positions
  * Compositor currently only asks for tiles from outermost frame
  * Window events are forwarded to the outermost frame's script. Should be routed to proper script via constellation.
  * Layout's sending of updated iframe sizes to constellation or size future (initial size only) as reflow is performed
constellation blocks on compositor before sending permission to paint to renderers