subdir implementation sometimes drop trailing slash, leading to 404

[anarcat]

okay, this is a really weird bug that i was aware of when we pushed that pull request in for the subdir feature, but since it's uncommon and easy to workaround, we still went ahead.

now i think i'm annoyed enough by it that i'll at least document it and hopefully @jcharaoui will magically fix it. :p

if i go on https://example.net/bookie/anarcat/recent - type a tag in the search form (say, toread), hit enter, the URL turns into https://example.net/bookieanarcat/recent/toread?count=50&page=0

Notice how the slash after bookie is now gone! If I hit reload then, i get a 404. If i visit a link and hit "back", i get a 404 as well.

i believe this is the only bug left with subdirs, except maybe #554 which i have not myself experienced.