Don't require ecb.
Hackaround for missing xcscope.

The latest xcscope I can find is a GitHub repository. Rather than deal
with the whole submodule mess, I'm just going to live without it on
platforms where it isn't an apt-get away.
Auto-install some packages.

Check for the presence of some packages that don't come with Emacs out
of the box, and install them if they are missing.

This makes it easier to get Emacs working when cloning this repository
for the first time.