(event_subscribe): Allocate the argument to notify_callback (arg) on the heap, not the stack, since event_subscribe's stack frame will not exist when notify_callback is invoked.
(event_subscribe): Allocate the argument to notify_callback (arg) on
the heap, not the stack, since event_subscribe's stack frame will
not exist when notify_callback is invoked.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome