Simplified captive_sandbox_spawn() prototype.

Simplified captive_sandbox_spawn() prototype.
Implemented 3-stage image_iochannel GIOChannel sequence for commits.
validate_CORBA_Environment(): CORBA Exception reporting is fatal
 - all its callers considered such case fatal anyway
corba_shutdown(): CORBA_ORB_destroy() errors ignored
 - it sometimes reports: a total of X refs to X ORB objects were leaked
   - FIXME - 1 ref per each sandbox child failure-restart cycle; why?
Disabled sandbox child shutdown process exit as it is killed by its parent
 - otherwise COMM_FAILURE occured on shutdown() method call by parent
Fixed heartbeat disable by sandbox_child_prepare_shutdown()
captive_sandbox_parent_query_vfs_retry(): Fixed exception memory leak