flip return value of button handlers

This is compatible with Javascript, and it also seems like a better
default; when people forget to think about return values in click
handlers, they should be consumed.

button.lua

@@ -1,7 +1,6 @@
 -- Simple immediate-mode buttons with (currently) just an onpress1 handler for
 -- the left button.
--- If the handler returns true, it'll prevent any further processing of the
--- event.
+-- If any applicable button handler returns true, it'll propagate the click to other handlers.
 
 -- draw button and queue up event handlers
 function button(State, name, params)
@@ -15,14 +14,14 @@ function button(State, name, params)
 end
 
 -- process button event handlers
-function propagate_to_button_handlers(State, x, y, mouse_button)
+function mouse_press_consumed_by_any_button_handler(State, x, y, mouse_button)
   if State.button_handlers == nil then
     return
   end
   for _,ev in ipairs(State.button_handlers) do
     if x>ev.x and x<ev.x+ev.w and y>ev.y and y<ev.y+ev.h then
       if ev.onpress1 and mouse_button == 1 then
-        return ev.onpress1()
+        return not ev.onpress1()
       end
     end
   end

edit.lua

@@ -163,7 +163,6 @@ function edit.draw(State)
                        end
                        schedule_save(State)
                        record_undo_event(State, {before=Drawing.before, after=snapshot(State, line_index-1, line_index+1)})
-                       return true  -- don't handle any other events with this mouse button press
                      end,
         })
       end
@@ -209,7 +208,7 @@ end
 function edit.mouse_pressed(State, x,y, mouse_button)
   if State.search_term then return end
 --?   print('press', State.selection1.line, State.selection1.pos)
-  if propagate_to_button_handlers(State, x,y, mouse_button) then
+  if mouse_press_consumed_by_any_button_handler(State, x,y, mouse_button) then
     -- press on a button and it returned 'true' to short-circuit
     return
   end