Return SIGCHLD handler to DEFAULT for children (perl)

Return SIGCHLD handler to DEFAULT for children (perl)

Remove the special SIGCHLD handler applied to the parent/listener
process from spawned child processes (drones) by setting child handler to
DEFAULT.  Otherwise, if an OpenSRF drone process spawns a sub-process,
the drone will execute the SIGCHLD handler meant for the Listener when
the sub-process dies, wherein hijinks ensue.

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