"chunk is already free" bug

Hello,

  I think I found the "chunk is already free" bug
  (seen in "fs-test 24" for example on FreeBSD at least).

  svn_fs__track_dbt() was called for a DBT that was not an
  svn_fs__result_dbt, but a DBT whose data was allocated in a pool. The
  attached patch fixes this, but I'm not sure if this is the "rigth"
  solution to this problem, 'cos I only had this afternoon to look into
  this and I don't see clearly whether it's OK to use this
  pool-allocated DBT here since the data is changed in the
  last_key_before() call.

  Anyway, hope this helps to someone more familiar with the libsvn_fs
  code.

cheers,
mitch

-- 
// RADICS Peter <mitch_at_lbcons.net> (http://lbcons.net)
//
// "If human beings don't keep exercising their lips, 
//  their brains start working." -- Ford Prefect