pin: Handle pins of multiple sources for a spec
pin: Handle pins of multiple sources for a spec

You can now add (and remove) pins for a spec file for a given source using
--source. At the moment these pins are still expected to be git repositories
that will be described and archived.

At the moment, the resulting version used for the pinned spec-file will be the
largest version number of all of the pins.

Signed-off-by: Si Beaumont <a0992b7f1f450b4c7716d34b81a2d6f0877ae11a@citrix.com>

djs55/planex,djs55/planex,djs55/planex