"lost sprint": Remove checking vs horizontal buffer.

Might consider for future:
The problems of the type lost-sprint, bunny seem to be client mechanics.
The ground-modifiers apply and stay valid during jump, thus turning off 
sprint for attacking makes sense.

So i revert the statement about "could be worth a ticket" for the
moment. However with looking forward to have a Minecraft API, it could 
could be appropriate to provide something to allow server-side checking,
yet again finding the right ground modifier needs knowledge of the 
exact moves the client did, so client side could change to send all the 
transition events as suggested before.
SF: Set initial hbuf to 0. Need new concept/discussion.

Setting to something on creation of data is ineffective, because it gets
set to 0 on passable violations.

Keeping the buffer means other abuse potential.

Probably better postpone until re-design/removal of the buffer concept.
SF: Optimization and fixes with bunny and permchecks.

* Currently bunny applies very often on sprinting, thus it can be pre-
  checked before permchecks, and if necessary re-checked after 
  permchecks.
* Remove heuristic permchecks, since the above should do better.
* Fix bunny not trigger for assumeonground && jumpphase == 0.

Further we will try to get rid of the horizontal buffer as we know it,
 confining it to special cases. However we have to extend bunny hop to
 apply without sprinting as well. Might need a more general concept
 for ground-move-modifiers and friction to achieve it.