Add background color field to Scene

[ibnc]

This is in order to complete servo/servo#140.

So, I've forked the repo, and made some changes, but whenever I try to build I get an error saying "can't find crate for 'geom'." I'm rather new to rust, and can't seem to get geom to install with rustpkg--as there is no main.rs/lib.rs/etc file.

Does there exist documentation on contributing to servo submodules?

Also, anyone have any objections to me importing azure, and having the background_color field just be a AzColor?

Help would be greatly appreciated!

[pcwalton]

Try using the main Servo makefile after you make changes. It may help to configure Servo with ./configure --disable-manage-submodules.