Add 'description' to the scraped error message from tomcat.

This is a small change to try and make the error a bit more descriptive. It changes error messages from (for example);

    SolrError: [Reason: /solr/mlt/]

To;

    SolrError: [Reason: /solr/mlt/, The requested resource (/solr/mlt/) is not available.]

When pysolr hits urls like this;

![screen grab](http://f.cl.ly/items/0h3N2T0j3F3D2823470t/Screen%20Shot%202012-05-19%20at%2015.29.39.png)

Couple of questions;
1. I'm not sure how best to test this.
2. In this case the HTTP status code (404) would be useful to know. Should it be included too?