fix 'timeit' in headless mode

res/scripts/stdlib.lua

@@ -15,6 +15,7 @@ if test then
     test.new_world = core.new_world
     test.close_world = core.close_world
     test.reconfig_packs = core.reconfig_packs
+    test.tick = coroutine.yield
 end
 
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res/scripts/stdmin.lua

@@ -34,11 +34,11 @@ end
 
 
 function timeit(iters, func, ...)
-    local tm = time.uptime()
+    local tm = os.clock()
     for i=1,iters do
         func(...)
     end
-    print("[time mcs]", (time.uptime()-tm) * 1000000)
+    print("[time mcs]", (os.clock()-tm) * 1000000)
 end
 
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