[ticket/12852] Make get_url_parts handle get variable with no value

PHPBB3-12852
[ticket/12852] Remove whitespace

PHPBB3-12852
[ticket/12852] Add space after if

PHPBB3-12852
[ticket/13031] Guess with all mimetype guessers and pick best guess

PHPBB3-13031
[ticket/13031] Slightly change behavior of choose_mime_type and add unit tests

The mime type 'application/octet-stream' will still always be overwritten by
proper guesses. However, guesses with guessers that have a higher priority
will now overwrite previous guesses even if the mime types of these guesses
had a slash in them.

PHPBB3-13031
Merge pull request #2919 from Senky/ticket/12852

[ticket/12852] Make get_url_parts handle get variable with no value

* Senky/ticket/12852:
  [ticket/12852] Add unit tests
  [ticket/12852] Add space after if
  [ticket/12852] Remove whitespace
  [ticket/12852] Make get_url_parts handle get variable with no value