extend overridable graphics/sounds to 8 of each, for lua scripters who really like having their own sprites/sounds. these should not be used in the engine.
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.