plugins/Seen: Use an IrcSet to gather the seen nicks instead of a list.  This makes commands like '@seen *amessan' work as expected.
plugins/Seen: Use an IrcSet to gather the seen nicks instead of a list.  This makes commands like '@seen *amessan' work as expected.

frumiousbandersnatch/supybot-code,kblin/supybot-gsoc,ProgVal/Limnoria-test,raboof/supybot,buildbot/supybot,mazaclub/mazabot-core,haxwithaxe/supybot,mazaclub/mazabot-core,ProgVal/Limnoria-test,Ban3/Limnoria,jeffmahoney/supybot,Ban3/Limnoria,prashantpawar/supybot-rothbot