Add Smaller Limit Options to Apache Solr Cron Indexing

In some cases, a node may have a very large number of comments (my site typically has about 300), and using the apachesolr_commentsearch module only increases the processing, since each comment is a document. I'm getting memory errors when trying to index my site with 10 nodes/execution.

I've added 1 and 5 nodes/execution options in the attached patch.