Implement UIManager:unschedule(action). Fixes #1007.

frontend/device/generic/device.lua

@@ -90,7 +90,7 @@ function Device:onPowerEvent(ev)
         self.screen:setRotationMode(0)
         Screensaver:show()
         self:prepareSuspend()
-        UIManager:scheduleIn(2, function() self:Suspend() end)
+        UIManager:scheduleIn(10, self.Suspend)
     elseif (ev == "Power" or ev == "Resume") and self.screen_saver_mode then
         DEBUG("Resuming...")
         -- restore to previous rotation mode
@@ -113,6 +113,8 @@ function Device:Suspend()
 end
 
 function Device:Resume()
+    local UIManager = require("ui/uimanager")
+    UIManager:unschedule(self.Suspend)
     self.screen:refresh(1)
     self.screen_saver_mode = false
 end

frontend/ui/uimanager.lua

@@ -191,6 +191,16 @@ function UIManager:scheduleIn(seconds, action)
     self:schedule(when, action)
 end
 
+function UIManager:unschedule(action)
+    for i = #self._execution_stack, 1, -1 do
+        local task = self._execution_stack[i]
+        if task.action == action then
+            -- remove from table
+            table.remove(self._execution_stack, i)
+        end
+    end
+end
+
 -- register a widget to be repainted
 function UIManager:setDirty(widget, refresh_type)
     -- "auto": request full refresh