* shoes-off.el (shoes-off/handle-request): Fix a bug introduced in 930ec70

Synchronize channels between the remote client and shoes-off client only
when for PRIVMSG. For other commands, it is done "automatically".

e.g. TOPIC command:
<remote> /topic new topic
Both the remote and shoes-off RCIRC clients see
*** remote TOPIC this is a new topic
* shoes-off.el (shoes-off/handle-request): Use `shoes-off/send-to-channel'
rather than rolling my own.
(shoes-off/send-to-channel): Use RCIRC primitives to retrieve or to create
the buffer if necessary before sending any data.