Let solrconfig.xml configure the SolrDispatchFilter to handle /select

The major reason to make everythign use the SolrDispatchFilter is that we would have consistent error handling. Currently,

SolrServlet spits back errors using:
PrintWriter writer = response.getWriter();
writer.write(msg);

and the SolrDispatchFilter spits them back using:
res.sendError( code, ex.getMessage() );

Using "sendError" lets the servlet container format the code so it shows up ok in a browser. Without it, you may have to view source to see the error.

Aditionaly, SolrDispatchFilter is more decerning about including stack trace. It only includes a stack trace of 500 or an unknown response code.

Eventually, the error should probably be formatted in the requested format - SOLR-141.