Normalize url

This patch implements the net (after conversation) functionality of the following two bullets on the Walker Project Plan

* Ensure we normalize URLs (NOTE: some of these may be a non-issue, just want to check them):
* Configurable parameter exclusion (case insensitive) with defaults: jsessionid, phpsessid, aspsessionid

Ah, yeah that's pretty confusing. Maybe when we devote more work to URL normalization we can fork it or write something of our own. Yeah a comment here to clarify that sounds good.