core: avoid casting data to string if it is already an instance of basestring, in irc.reply.

src/callbacks.py

@@ -830,6 +830,7 @@ class NestedCommandsIrcProxy(ReplyIrcProxy):
         # action=True implies noLengthCheck=True and prefixNick=False
         self.noLengthCheck=noLengthCheck or self.noLengthCheck or self.action
         target = self.private and self.to or self.msg.args[0]
+        if not isinstance(s, basestring): # avoid trying to str() unicode
             s = str(s) # Allow non-string esses.
         if self.finalEvaled:
             try: