Highlighting ConstantScore Queries

[Mark Miller]

A recent change made wildcard queryies un-highlight-able.  This had 
already happened to prefix queries.

Lucene-1424 and Lucene-1425 will make it so that solr will again be able 
to highlight these queries when using the Span Highlighter.

When/If those issues are resolved, I'll make an issue for the necessary 
solr changes (no rewriting the query if using the Span Highlighting 
scorer, etc).

- Mark