Generating gtk-doc on nicobar

[Ethan Blanton]

Mark Doliner spake unto us the following wisdom:
> I'm kinda thinking this is a bad idea and we should just stop
> generating API docs automatically for head. We can build and upload
> docs manually as part of our release process, and we can list steps
> for people to build their own docs locally.

I am inclined to agree that we don't want to build on nicobar.

Perhaps the 'make dist' target can compile the docs into a tarball
that we can just untar in some special place?

Ethan