Use normalize_uri (@wchen-r7)

Instead of editing the datastore['PATH'], use normalize_uri.

Since the purpose of this module is quite fuzz-like, I didn't want to
apply the normalize_uri to the whole uri -- the original code merely
applied to datastore['PATH'] (which seems like it should be
datastore['URI'] really) and then added on a bunch of other stuff to
test for traversals.