Bug 507: Reset stuff upon player death

Bug 507: Reset stuff upon player death

If Tux dies while he is subject to increased gravity (jump_early_apex), he
retains this attribute during the dying sequence, which looks weird.

I will attach a patch that resets the safe_timer and gravity and, for
consistency, resets the invincibility upon death instead of checking !dying
when creating sparkles.

Resolves #507. Thanks to Matt McCutchen for this patch.

git-svn-id: http://supertux.lethargik.org/svn/supertux/trunk/supertux@6290 837edb03-e0f3-0310-88ca-d4d4e8b29345