Use SolrIndex->getIndexName() consistently

That's important in case we need to disambiguate the index, e.g. when multiple copies of the same codebase run on the same environment and server.
Example implementation:

function getIndexName() {
	return preg_replace('/[^\w]/i', '-', __FILE__);
}
Merge pull request #59 from ss23/3.0-compat

Use SolrIndex->getIndexName() consistently