Use full string for sidFuel and avoid string concatenation Fuel as in fuel for saucer, landgun, flamethrower, icegun. Old string was built with like this: sidFuel + ": " + fuel + "%". New string us built with proper format string instead

Lua scripts for engine testing. These scripts are the same as other Lua scripts
in Hedgewars, but you ought to call `EndLuaTest(TEST_SUCCESSFUL)` or
`EndLuaTest(TEST_FAILED)` when the test is completed.