C SIGHUP handling and config reloading

C SIGHUP handling and config reloading

Sending the HUP signal to a C Listener process now results in the
following:

 * Reload the opensrf_core config
 * update the log file level
 * kill idle child processes
 * child processes that are active when the signal is received are
   tracked and killed once they become idle.
 * New children are spawned per the min child settings

The primary use case for these changes is temporarily changing the log
level for a given service for debug purposes.  It may also
be used, for example, to gracefully recover excess RAM consumed by a
child process.

opensrf.xml (opensrf.settings config) is not reloaded, so min/max child
settings will not be affected.

Signed-off-by: Bill Erickson <berick@esilibrary.com>