Add iterateHashTable function.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Remove unnecessary rc assignments.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Add cast for END_LISTENER_LIST.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Fixup RC accounting.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>