Fix tabs sometimes not closing using the middle mouse button

Review Request #111610 - Created July 19, 2013 and discarded - Latest diff uploaded

Diego Soenens
If the mouse moves even 1 pixel while the middle mouse button is being pressed/clicked to close a tab it causes KTabBar to not emit mouseMiddleClick() if isMovable() == true.
As a result the tab doesn't get closed and the user has to try again and this can happen a few times in a row if the mouse has a "hard" middle mouse button. Quite annoying :(.

According to the comment it's a "compatibility feature for old middle mouse tab moving" so I'm not exactly sure if this should even be fixed to begin with and whether Rekonq is the place to do it in this case.

Edit: not sure why my diff isn't working?
Been running this patch for a few hours. Everything seems to work as intended.