ircdb: Fix 'IrcUser.nicks' on non-lowercase network names

This dict was filled with IrcString keys, which is hashed
as lowercase, so when queried with a non-lowercase string,
the key would not be found, and lead to very confusing errors.

src/ircdb.py

@@ -218,7 +218,8 @@ class IrcUser(object):
         else:
             self.hostmasks = hostmasks
         if nicks is None:
-            self.nicks = {} # {'network1': ['foo', 'bar'], 'network': ['baz']}
+            # {'network1': ['foo', 'bar'], 'network': ['baz']}
+            self.nicks = ircutils.IrcDict()
         else:
             self.nicks = nicks
         self.gpgkeys = [] # GPG key ids