Fixed a bug and some confusion with ACLChecklist::fastCheck()

Fixed a bug and some confusion with ACLChecklist::fastCheck()

- Added cbdataReferenceDone(accessList) call to fastCheck() in the
  "if finished()" block.

- peerAllowedToUse() was setting accessList = NULL after calling
  fastCheck().  Since neither fastCheck() nor peerAllowedToUse()
  were calling cbdataReferenceDone(), the cbdata lock_count would
  never decrease and eventually hit an assertion.

- In general, the fastCheck() callers do not need to call
  cbdataReferenceDone, nor set accessList to NULL.  The
  cbdataReferenceDone() call should always happen in fastCheck().
  If not, it will happen in the ACLCheckList destructor.

- It might be even better if fastCheck() called cbdataReference()
  as well, to avoid this situation where locking happens in one
  place and unlocking in another.  This is future work, however.