Fix sinegun dealing 1 damage when shooting straight up. Reduces sine gun knockback strength by 1.25% This was caused by AmmoShove, which had a strenght which was *right* above the threshold for fall damage.

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.