Duke3D: Superjump out of water bug

As reported in several threads on the duke4 forums.

If you press the jump key twice in quick succession while standing in a water sector (lotag 1), sometimes the game allows you to jump much higher than you are supposed to, even compared to jumping on solid ground. The following video demonstrates this, it should be pretty obvious:

https://www.youtube.com/watch?v=Z3QvXsaOZA0

This problem started occuring with r7428 (commit d060ca95) aka. the controversial clipping changes.

Test map: superjump_bug.map