Add support for re-exec without loosing IRC connection

This allows you to execute a new version of the bot, while preserving the connection to the IRC server.

It is done by calling exec with the same name and arguments it was originally executed with, and passing on the file descriptor of the socket to the IRC server. A new version of the script will then take over the process, and reuse the socket to the IRC server.

To make this possible, the connect and parse methods of the IRC class in Cinch had to be overridden.