Instead of letting buttons determine the relative position
of their menus, a workaround only used by Statusbar segments,
open them all uniformly for a nice, consistent UI.
Passing a rect to popup() now routes to open_button_menu(), an
analog to open_menubar_menu(), which adjusts the menu's popup
position in the same way. Fixes button menus obscuring the buttons
which spawn them and jutting out at odd corners depending on screen
position.
35e557c657