Fix a pool use bug in BDB lock code, allocate lock passed to callback
in the result pool.

* subversion/libsvn_fs_base/lock.c
  (struct lock_args): Add pool.
  (txn_body_lock): Allocate lock in result_pool.
  (svn_fs_base__lock): Pass result_pool, pass path allocated in
   result_pool, destroy trail-pool.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1585698 13f79535-47bb-0310-9956-ffa450edef68