Added support for unix-dgram transport for node > 0.7 and udp6

I'm using unix-dgram from Ben Noordhuis to get the support for unix dgrams > 0.7.

The SysLogger.prototype.transport had to be refactored to be accepting strings instead of the function in order to accept udp4, udp6, and unix_dgram.

It accepts the address property in the config as the path to the socket.  Its a little misnamed in that case, but LMK if you want to change the PR.

An integration test was also added to support this.