What solved it for me (no setstage or quest commands needed):
1.) Go to the Concord shop (where Stranger is) *
2.) Use the "move.to player" command on Old Paul and bring him there
3.) Done. He will start a dialog with you
* If you don't know how to use the move.to command or any command for that matter, here's some help:
1.) Find Old Paul and make sure he's appearing on your screen.
2.) Press ~ (this button will vary from country to country, please look up what yours is). This opens the command interface-thing.
3.) Click on Old Paul. Now a weird id number with letters will appear. That's his id. Remember it.
4.) Go to the Concord shop (where Stranger is).
5.) Open the command interface again and type in "move.to player x" without the quotes. Instead of x, write down his id.
6.) Done. He will pop-up and start a dialog with you.