wikipedia: fix urlparse usage & handle Special: namespace

[SnoopJ]

Description

Closes #2573.

This changeset corrects errant usage of urllib.parse.urlparse() in the wikipedia plugin, fixing a regression introduced by #2414. This fix prevents namespaces from being erroneously discarded.

In the process of this fix, I discovered that the Special:* namespace is a special case as far as the MediaWiki API is concerned, queries to the API for pages in this namespace don't do what you might expect, so these pages cannot be located and turned into snippets for IRC. So, instead, the URL rule ignores these pages, and issues a specific explanation if a user tries to query them using a command.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make lint and make test)
• I have tested the functionality of the things this change touches

[dgw]

As I've already played with the patched plugin in your bot's test channel, I only have nitpicks left.

[dgw]

Thought this PR had been made ready to go, but apparently not. Good to squash, and if you're feeling extra on-top-of-things you can make sure the draft changelog you've been working on reflects both bugfixes from here. 😉