mediawiki.Title.test: Add test for space collapsing

mediawiki.Title.test: Add test for space collapsing
* When I first passed "Foobar___.js" to mw.Title and saw that it was stripping away (some) spaces, I thought it was a bug (since extension is part of the title and should be kept as is). Anyway, as it turns out it's not stripping them away because they are between 'title' and 'extension', it's a general rule that there should not two or more spaces next to each other in a title. Adding test to assert and confirm this behavior.