file-utils: URL normalization and more xspec tests

Without URL-normalization, px:fileset-add-entry couldn't add 8.3-formatted
Windows-filenames. For instance, "Documents and Settings" becomes
"DOCUME~1", which wasn't recognized as the same as "DOCUME%7E1"
in pf:relativize-uri.
Merge pull request #20 from daisy-consortium/uri-normalization

file-utils: URL normalization and more xspec tests