This is the "gather" module.  This module is used to gather packages and their
dependancies from repositories and lay them out in a logistical manner.  A
comps file will determine what top level packages to pull in.
We're probably going to steal some code from yumdownloader and reposync, and
use yum.comps to parse the comps file.

ROADMAP

a) Use yum.comps to parse our comps file to generate a list of packages to
   depsolve and download.
b) Wire up something to actually download the package list and write it out
   somewhere.

CONSIDERATIONS

Probably should allow continuing if a package isn't found in a particular arch.
Probably should error if a package isn't found in any arch.

QUESTIONS

Do we createrepo here, once we've gathered our packages?