Fixed https://github.com/snej/MYNetwork/issues/9

 - ARC is more aggressive than retain/release/autorelease used to be, and it is causing occasional issues on disconnect
 - It appears that TCPConnection's "sAllConnections" static mutable array variable, which would solve this, is never (and has never actually been) initialized to an real NSMutableArray object.
 - Adding that initialization appears to fix the issue.