Try to parse command line argument as file names

… when parsing as an absolute URL (without a base) fails.

Previously, arguments were parsed as URLs with the current working directory
converted to an URL and used as the base URL. This mostly worked for
relative filenames, except that `?` and `#` had a special meaning
and needed to be percent-encoded.

Fix #3340.
Give explicit file: URLs for reftests. Allow specifying a fragment id

The previous commit made #top be considered part of the file name in
../html/acid2.html#top
Merge pull request #3365 from SimonSapin/command-line-argument-filenames

Try to parse command line argument as file names