Technical notes on version 1.20 19May02
                       19 May 2002
                       Kern Sibbald

General:
- Modified rwlock to accept multiple nested write lock
  requests.

Changes submitted this submission:
- Modified the cats directory to use the new rwlock mechanism
  in place of P() and V(). 
- Defined db_lock(mdb) and db_unlock(mdb). They are in effect
  transaction locks.