Improve package data loading and error handling.

Review Request #7733 — Created Nov. 3, 2015 and submitted — Latest diff uploaded

Information

rbpkg
master

Reviewers

When looking up a package from the repository, we now pass the base path
in, helping to ensure the relative URLs are all correct.

We also listen for errors in the lookup, and represent that with a more
useful exception.

Unit tests pass.