[asdf-devel] Pushed proposed fix for Xach's bug

Passes all of the unit tests (including the new one based on Xach's test case). Please, all of you, have a peek at the diffs (possibly I should have squashed the changeset to make this easier, sorry), and the commit message, and test it as soon as possible. I have not bumped the version number, as this is still a work in progress subject to review. best, r