On Mac, "return" key should trigger colored button on windows

[Ryan]

Whenever a window has a colored button, such as the "connect" button in the site manager or the "ok" button in the signature verification window, the return key should trigger that button. Except of course when you're in a multi-line text view.

Less consequentially, standard behavior also dictates that one of the buttons probably has a border around it (highlighted) and the space bar will trigger that button. This highlighted state can be moved between the next and previous buttons in the window by using tab and shift+tab respectively.