Show the "Move associated talk page button" on special:movepage if there are subpages...

Show the "Move associated talk page button" on special:movepage if there are subpages in the corresponding talk page
that could be affected by it, even if the base page being moved does not have a talk page.

(I just had a discussion with mindrones on irc about how the current behaviour with the talkspace subpages sometimes being moved by "move subpages" button and sometimes not depending on if current page had a talk page (and thus had the move assoc. talk button auto checked) was really confusing to the average user.)

As an aside, Special:Movepage could probably do with some refactoring ;)