Channel joiner dialog does not allow you to join a valid channel

The initial popup when connecting to a server:

![cc-complete](https://f.cloud.github.com/assets/855009/1233479/93b75106-292c-11e3-9964-c542fbeb632c.png)

Will not allow you to join the channel "#", which is valid everywhere and in the RFC 1459. 

   Channels names are strings (beginning with a '&' or '#' character) of
   length up to 200 characters.  Apart from the the requirement that the
   first character being either '&' or '#'; the only restriction on a
   channel name is that it may not contain any spaces (' '), a control G
   (^G or ASCII 7), or a comma (',' which is used as a list item
   separator by the protocol)


Additionally, the join channel dialog (not the one that appears on server connection) allows you to join '#' as it should. So this behavior just puts the initial connection dialog into line with behavior present elsewhere.