irclib: Log the server's error message on SASL failure.

Author: progval

src/irclib.py

@@ -1992,8 +1992,8 @@ def do903(self, msg):
             self.endCapabilityNegociation(msg)
 
     def do904(self, msg):
-        log.warning('%s: SASL authentication failed (mechanism: %s)',
-                self.network, self.sasl_current_mechanism)
+        log.warning('%s: SASL authentication failed (mechanism: %s): %s',
+                self.network, self.sasl_current_mechanism, msg.args[-1])
         self.tryNextSaslMechanism(msg)
 
     def do905(self, msg):