Bail out when loading an non-existant plugin without breaking things

irc.py

@@ -106,7 +106,8 @@ class PluginManager(object):
         plugins.refresh()
         if not self.loadedPlugin(pluginName.lower()):
             if not self.pluginExists(pluginName.lower()):
-                raise ValueError("No such plugin.")
+                self.prnt("No such plugin " + pluginName)
+                return
             
             pClass = plugins.getPlugin(pluginName.lower())