Remove "loser" messages in challenges
The point of challenges is not to "win", but to reach a highscore, so we need not to rub failure into the player's face.
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.