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

Hm, yeah I had been thinking matching case-insensitive would be better, but I'm on the fence about it. I suppose since it's easier it's okay if we leave it case sensitive.