- Move the definition of LOCK_DEBUG back to sys/lock.h from sys/_lock.h.

- Move the definition of LOCK_DEBUG back to sys/lock.h from sys/_lock.h.
- Change LOCK_DEBUG so that it is always on if KTR is compiled in
  regardless of the state of KTR_COMPILE.  This means that we no longer
  need to include sys/ktr.h before sys/lock.h to ensure a valid setting
  for LOCK_DEBUG.
- Change the use of LOCK_DEBUG so that it is now always defined and its
  value is used instead of merely its definition.  That is, instead of
  #ifdef LOCK_DEBUG, code should now use #if LOCK_DEBUG > 0.
- Use this latest to #error out in sys/mutex.h if sys/lock.h isn't
  included before sys/mutex.h to ensure that the proper versions of the
  mutex operations are used.
- As a result of (2) sys/mutex.h no longer includes sys/ktr.h in the
  KERNEL case.

Requested by:	bde (1)