Hello developers,

I discovered recently that the irc client `rcirc', although has an
max-message-length set, but it simply uses (length str) for detecting
the output length, which is not desirable for multibyte users because
usually our characters encode to more than one byte, and this causes an
error that the client actually sends out more bytes than the standard
has required (512 bytes to my understanding).

This limit is easily reached since chinese characters are usually
encoded with 3 bytes for one character.

By this error, if the server truncates the result string simply by
bytes, then it's known to cause the string to become entirely scrambles
for xchat.

I'm attaching a patch to perform an binary search for multibyte strings,
and this patch should not have any penalties for original ascii users
since it begins with a (multibyte-string-p) to decide which style to use.