retain/autorelease the dictionary when seeding completes, instead of creating a new dictionary

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14035 f4695dd4-2c0a-0410-b89c-da849a56a58e
make the children in a FileListNode a property

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14036 f4695dd4-2c0a-0410-b89c-da849a56a58e