MediaWikiClient: fix compile warnings

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add an interactive test for the MediaWikiClient

This makes testing (and especially debugging!) much easier.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
MediaWikiClient: adjust to new MediaWiki engine versions

The new MediaWiki engine used by the Fiji Wiki does a few things a
little different than before: It requires the value of the submit
button to be passed, it redirects via 302 to the referrer page, and
it requires cookies to be set all the time.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'mediawiki-upgrade'

This should fix the plugin-list-parser job updating the Fiji Wiki from
stable Fiji releases.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>