DistroSeries Binary Package page dependent on publishings

[Michael Nelson]

This is a longer-term proposal coming out of a short-term fix for bug 257614.

The initial issue in bug 257614 was that the pages main content was blank if the DSBP didn't have any published packages.

Example URL:
https://launchpad.net/ubuntu/feisty/+package/libgimme-codec-bin

but the underlying issue seems to be that the DistroSeries Binary Package page is dependent on data that it may not have for its main content. I don't yet have the broader picture, but to me it would make sense that the DSBP page should only be dependent on data that it is guaranteed to have (or at least, guaranteed to have eventually).

Also, the fix for bug 257614 was to return the string "No summary available for blahblah" when the DSBP's summary method cannot get the data it needs, but really this is logic that belongs in a view. The DSBP#summary method should return None (as it did), and the view should use this to determine the result the user sees. I didn't do this in the fix because it seems that the launchpad views are currently very thin, having only one context object, and the request object.