Fix #922: Bindings generator generates .pyc files
auto merge of #1735 : tgkokk/servo/python-write-bytecode, r=kmcallister

Forgot to actually claim #922. I hope no one is working on it.

I removed `PYTHONDONTWRITEBYTECODE=1` from every relevant file and I added code for removing `*.pyc` files in `clean-script` in `mk/clean.mk`. You might want to move the main logic into a function like `REMOVE_PYC_FILES`, since the files will exist eventually in other trees under `/src`. I used `find` in order to find all `*.pyc` files, since they might be in other subdirectories.

This is my first PR, so feel free to give me any feedback you might think is necessary.
Implement JSManaged for DOM objects.
auto merge of #1591 : jdm/servo/jsmanaged, r=Ms2ger
Initial unmodified dump of Gecko's union codegen.
Implement WebIDL union support.
Clean up TrySetTo interface to avoid mutable outrefs.
Remove commented bits that aren't necessary.
Remove methods from IDL that don't do anything useful.
Move HTMLDocument members to Document.
Remove HTMLDocument.
Remove document::DocumentType (fixes #1730).
Remove DocumentTypeId.
Move from gfx::opts to servo_util::opts.
auto merge of #1739 : Ms2ger/servo/document-cleanup, r=jdm

The specs currently have only Document; this may well change, but the split won't be along the lines we've implemented right now. In the meantime, this simplifies our code quite a bit.
Make JSVal conversions actually fallible.
Address review comments. Fix union conversion result mistakes introduced in refactoring.
auto merge of #1738 : saneyuki/servo/opt, r=kmcallister

I think gfx/opts.rs should be placed to more general place.
auto merge of #1689 : jdm/servo/unions, r=kmcallister

Seven hours on a train without internet will do this to you. Fixes #541.
layout: Run assign-widths in parallel.

5% layout speedup on mobile Wikipedia.