Test for another form of NICK

Freenode sends NICK in a form not yet supported:

    :old_nick@host NICK :new_nick

This test proves failure in that format.
Allow optional colon(:) before new nick in NICK

This is to allow for networks (such as freenode) that send NICK in the format:

    :old_nick@host NICK :new_nick
Merge pull request #11 from meshy/freenode-nick

Nick change failure on freenode