Normalize history cache keys - redux

[croxton]

1. Since LocalStorage is bound to the origin (domain/protocol/port triplet), we can normalize the URL format used as a key for a history snapshot to reduce cache misses for the same URL but referenced differently. E.g.: https://mysite.com/about, /about and /about/ are normalized to /about. Cache misses also mean that the scroll position of the previously visited page is lost, which can result in unexpected scroll jumps that are hard to track down.

2. Prevent potential key collisions in boosted relative links, by converting the href to a fully resolved root-relative path. E.g. a boosted anchor shoe.html in the directory products becomes /products/shoe.html.

3. As IE11 doesn't understand URL, we silently catch the exception and return the unadulterated path. This is safer than messing about with a regex polyfill.

4. Adjust the boosted element hx-disinherit sanity check test to check for the fully-resolved href of the boosted anchor.