Fix button press behaviours. On LeaveNotify, make the button no longer pressed....

Fix button press behaviours.  On LeaveNotify, make the button no longer pressed.  On MotionNotify, only make it hovered if no button is pressed down.  On EnterNotify, make it hovered or pressed as appropriate.

This fixes case where you left-click and hold on a button, then right click to open the menu - this used to leave the button in a pressed state.