Polls: Make nick matching case-insensitive

This prevents the same nick from voting twice by changing
the capitalization

plugins/Poll/plugin.py

@@ -149,7 +149,10 @@ class Poll_(callbacks.Plugin):
             )
 
         self._polls[(irc.network, channel)][poll_id] = Poll(
-            question=question, answers=dict(answers), votes={}, open=True
+            question=question,
+            answers=dict(answers),
+            votes=ircutils.IrcDict(),
+            open=True,
         )
 
         irc.replySuccess(_("Poll # %d created.") % poll_id)

plugins/Poll/test.py

@@ -73,6 +73,11 @@ class PollTestCase(ChannelPluginTestCase):
             "voter1: Error: You already voted on this poll.",
             frm="voter1!foo@bar",
         )
+        self.assertResponse(
+            "vote 1 Yes",
+            "VOTER1: Error: You already voted on this poll.",
+            frm="VOTER1!foo@bar",
+        )
 
         self.assertRegexp(
             "results 1",