Don't let reddit users PM to '/u/' prefaced users

This is probably not a big deal, but at the moment if you PM the bot to tip another user on reddit, and you include /u/ prefixed to the user's name, the bot will send coins to an account that can't exist. For instance: 
    !tip /u/jwinterm 1
would send coins to reddit:/u/jwinterm, but '/' is not a valid character for reddit usernames. This change presumes that the sender intended to send funds to jwinterm and strips of the '/u/' preceding the actual username.

tipbot/modules/reddit.py

@@ -160,6 +160,9 @@ class RedditNetwork(Network):
             while '' in cmd:
               cmd.remove('')
             cmd[0] = cmd[0].strip(' \t\n\r')
+            if cmd[0] == u'tip' and cmd[1][0:3] == u'/u/':
+                log_info("Subbing out /u/ from username")
+                cmd[1] = cmd[1][3:]
             log_info('Found command from %s: %s' % (link.identity(), str(cmd)))
             if self.on_command:
               self.on_command(link,cmd)