[Yum] pkgpolicy configuration parameter

[seth vidal]

> It may help saving the line number in the data structure
> along with the data retrieved from the config file and sort
> the entries by that.  Would it be too difficult to implement?

it would mean subclassing or completely dropping configparser and
rewriting it all on my own. So yah, that sounds like 'teh suck' and not
worth it.

the way the metadata is being imported now it will take some work to
make pkgpolicy=last work better. Scoring a repository will actually be a
lot easier now.

-sv