Fix misleading log formatting when /msg'ing from a channel window.
When doing "/msg foo bar" in a channel, we used to log "<foo> bar"
in the channel log. This is very misleading, since it looks as if
'foo' said it rather than sending it *to* foo. This commit changes it
to "<-> foo> bar", which looks a bit odd to me but it's consistent
with what gets shown in the ircview.
This partially fixes the complaints in bug 100369
. The other part of
that bug is logging the message in the recipient's log
instead of the channel's, but that's apparently quite hard.