Fix display of pending follow requests.

Fix display of pending follow requests.

I had misunderstood the Mastodon docs' description of
Relationship::requested, which said "Do you have a pending follow
request for this user?". It turns out that means _you_ have requested
to follow _them_, not the other way round.

The other way round is also represented in this record, as the
'requested_by' field (mirroring followed and followed_by). Apparently
it's been in the server code for over a year, but accidentally left
out of the documentation until last month.