The GPG key for yum.postgresql.org was in the wrong directory,
and as written, would have only supported postgres 9.2 anyway.
I looked at the yum rpms for a few other versions besides 9.2,
and they appear to be using the same GPG key. So this commit
assumes that they all are doing so, and it sets things up
accordingly. Hopefully this will make the yumrepo support
compatible with other versions of postgres besides 9.2, but I
haven't added that to the actual test matrix yet.
Thanks to some tricks I learned from Nan Liu and Dan Bode, I was
able to figure out a way to move all of the new version-related stuff
back into the params class, and clean up some of the if/_real stuff.
Basic tests for centos6 + pg 9.2 are passing.
This commit creates a new class called `package_source_info`,
which has some initial framework for managing the postgresql.org
yumrepo. It also serves as a container for the 'version'
variable that is needed by the 'platform' class in order to
use other versions of postgres besides the system default.
