`git annex p2p --pair` implemented, using Magic Wormhole codes
that have to be exchanged between the repositories being paired.

It looks like this, with the same thing being done at the same time
in the other repository.

	joey@elephant:~/tmp/bench3/a>git annex p2p --pair
	p2p pair peer1 (using Magic Wormhole) 
	
	This repository's pairing code is: 1-select-bluebird
	
	Enter the other repository's pairing code: (here I entered 8-fascinate-sawdust) 
	Exchanging pairing data...
	Successfully exchanged pairing data. Connecting to peer1...
	ok

And just that simply, the two repositories find one another, 
Tor onion addresses and authentication data is exchanged, and a git remote
is set up connecting via Tor.

	joey@elephant:~/tmp/bench3/a>git annex sync peer1
	commit  
	ok
	pull peer1 
	warning: no common commits
	remote: Counting objects: 5, done.
	remote: Compressing objects: 100% (3/3), done.
	remote: Total 5 (delta 0), reused 0 (delta 0)
	Unpacking objects: 100% (5/5), done.
	From tor-annex::5vkpoyz723otbmzo.onion:61900
	 * [new branch]      git-annex  -> peer1/git-annex

Very pleased with this, and also the whole thing worked on the very first
try!

It might be slightly annoying to have to exchange two codes during pairing.
It would be possible to make this work with only one code. I decided to go
with two codes, even though it's only marginally more secure than one,
mostly for UI reasons. The pairing interface and 
[[instructions for using it|tips/peer_to_peer_network_with_tor]] is simplfied
by being symmetric.

(I also decided to revert the work I did on Friday to make `p2p --link`
set up a bidirectional link. Better to keep `--link` the simplest possible
primitive, and pairing makes bidirectional links more easily.)

Next: Some more testing of this and the Tor hidden services, a webapp UI
for P2P peering, and then finally removing XMPP support. I hope to finish
that by New Years.

Today's work was sponsored by Jake Vosloo on Patreon.