Fixes multiple issues
- Unicode errors when path contained non-ascii characters
- 403 errors when the current working directory was not a parent
directory of the static files
- "API abuse" super() implementation of the get() method was passed a
filesystem path instead of the url-path it was expecting
- The above could also lead to 403 errors on case-insensitive file
systems due to the way the base-class resolved and validated paths
with respect to self.root
87d46d079d