battery_box.lua: Make "srcstack" local (#525)

fgrosswig

2020-01-06 e90b28895cc28daf1a2e4fb772bd191400cf9e62

 technic/machines/power_monitor.lua

@@ -55,7 +55,7 @@
         local demand = sw_meta:get_int("demand")
         meta:set_string("infotext",
               S("Power Monitor. Supply: @1 Demand: @2",
               technic.pretty_num(supply), technic.pretty_num(demand)))
               technic.EU_string(supply), technic.EU_string(demand)))
      else
         meta:set_string("infotext",S("Power Monitor Has No Network"))
      end