tests/unix_sockets: Message->ResSet parser fixes

- Makes the parser not touch the original list, this enables one
  to use the function on the same message multiple times.
- Now takes into mention messages without all resources being
  transferred
tests/unix_sockets: Add a copy function to resource sets
tests/unix_sockets: Various updates

- Add a function for listening of changes
- Add support for partial messages
tests/unix_sockets_example: Update example with listening
tests/websockets_example: Sanify listening