Stop buffering and echoing CTCP requests and responses to other clients, except for /me

Stop buffering and echoing CTCP requests and responses to other clients, except for /me

Fix interaction between self-message and CTCP:
CTCP request from client A gets reflected from ZNC to client B, because
B has self-message. B sees this as a usual CTCP request (from the same
nick), and replies (to the same nick). ZNC reflects that response to A
because A has self-message, and also passes that response to IRC server,
which sends that response back to ZNC, which sends it to its both clients.

Close #1488