Tweaks to <failure> element

[David Malcolm]

On Tue, 2013-02-05 at 20:46 -0500, David Malcolm wrote:
> I'm trying to make my data-gathering more robust in the face of analysis
> failures, so am tweaking the <failure> element.
> 
> This commit is hopefully self-explanatory:
> https://github.com/fedora-static-analysis/firehose/commit/a889e8c68371f9110d45a936570ba231a28cb698
> 
...and it was still not flexible enough, so in the end I added a way of
supplying extra key/value pairs:
https://github.com/fedora-static-analysis/firehose/commit/a8b91b2bd67cb993406aea7983fb9ec1034afb13