The (soon to be) attached two patches for mod_dbd.c and mod_dbd.h
implement the following:

- convert expiry/time-to-live values to seconds

- make DBDKeep accept On and Off flag values

- add *_set flags to svr_cfg so that, for example, if the main server
  config specifies a non-default value, then a virtual host can
  override it
  - using the COND_PARAM(nmin, DEFAULT_NMIN) method would mean that
    a virtual host with an explicit setting of DEFAULT_NMIN via a
    DBDMin directive would be overridden by the main server's
    configuration; see mod_cache for example I cribbed from

- create a private memory pool for use by the reslist so that
  threads using the reslist via ap_dbd_acquire, etc. don't conflict
  with the owner of the pool (i.e., the pool passed in ap_run_child_init
  to dbd_setup)

- create a private memory pool for each ap_dbd_t, primarily so that
  prepared statements will be cleaned up when the connection is
  closed (otherwise they linger until the reslist or s->process->pool
  is destroyed, as do any cleanup callbacks registered in the
  apr_dbd_prepare driver code)

- wrap dbd_setup in separate logic for the init and retry cases
  - for the retry case, where init failed, create a thread mutex
    to serialize competing retries by multiple ap_dbd_open calls

- adds status values to log messages where possible

- prevent params being dumped to the log file when unable to connect
  to DB since this string may contain a DB password