deactive profiler when not in use; use newtype structs for task chans
workaround for broken cross-crate generic newtype structs

add issue number for newtype struct issue
cleaned up code in constellation to make it more maintainable
fix constellation being inundated with messages from script.
script task sent RendererReadyMsg after every reflow.
now, the renderer sends RendererReady at the appropriate time,
and _only_ if it doesn't have paint permission.
auto merge of #961 : tikue/servo/master, r=kmcallister

* Profiler is now close to a no-op when ```-p``` is not passed in
* The profiler's printing ```Timer``` now stops looping when the profiler is closed
* Most task ```Chans``` are now newtype ```structs```
* Some more ```Cell``` removals in places where ```spawn_with``` is appropriate