m_spanningtree Let the NICK handler change the nick of the incoming user on collision

Don't change it in DoCollision()
m_spanningtree Update comments around collision handling
m_spanningtree Replace #defines with references in DoCollision()
m_spanningtree Replace WriteLine() call with Unicast() in DoCollision()
m_spanningtree Return a bool from DoCollision()

The return value is true if the remote user or both have to change, false if only we have to change
m_spanningtree Don't accept NICK with 0 TS
m_spanningtree Only accept uuids in SAVE